
Qass. 
Book. 



COPYRIGHT DEPOSIT 



THE 



NAVIGATOR'S POCKET-BOOK 



THE 

NAVIGATOR'S POCKET-BOOK 

ffilleD witb pure <3olD 

ARRANGED FOR IMMEDIATE REFERENCE TO ANY 
NAVIGATION SUBJECT 

A Complete Guide and Instructor for the Navigator, containing Four 
Hundred Exhaustive Definitions in Addition to all the Practical Rules 
for Working Middle Latitude, Mercator's and Great Circle 
Sailings, as well as Finding the Ship's Place by Nu- 
merous Chart Considerations, and the Latitude and 
Longitude by Dead Reckoning, and by the 
Sun, Moon, Planets, and Stars 

ACCORDING TO SHORT, SIMPLE, AND RELIABLE METHODS 

Also the Arithmetic of Angular and Time Measure 
Compass Deviation, Nautical Astronomy 

Treatise on the Instruments of Navigation 

Law of Storms, Keeping the Log Book 

Magnetism. Logarithms, Measuring Altitudes 

Sumner's Method, Time, Weather, etc., etc. 

TOGETHER WITH DANGER- ANGLE AND OTHER TABLES 
BY ,/ 

CAPTAIN HOWAKD ^ATTERSON 

Formerly Professor of Naval Science at Brown's College, Principal of The New 
York Navigation School, and Commandant of the Haytien Navy 

AUTHOR OF 

"The Yachtsman's Guide,'" "Hand-book for Masters and ^M&be$? l ~ Xi Y&chting 
Under American Statute," " The Illustrated Nautical Dictionary," etc., etc. 

MUN i t*M 

NEW YORK 



CHARLES SCRIBNER'S 
1894 




HjZ/ 



y 



COPYRIGHT, 1894, BY 

CHARLES SCRIBNERS SONS 

7<? ■■■'; 



TROW DIRECTORY 

PRINTING AND BOOKBINDING COMPANY 

NEW YORK 



CHESTER W. CHAPIN, ESQ. 
Corinthian Yachtsman 

Steady at the helm from whatever quarter comes the wind 
Quick to catch either the caressing or threatening whisperings of the sea 
And novice in nothing that makes a sailor of the highest and truest 
American type 

THIS BOOK IS RESPECTFULLY DEDICATED 
BY HIS FRIEND 

THE AUTHOR 



PREFACE 

There are many voluminous and bewildering works on the 
subject of navigation, but up to the present time there has not 
existed a series of short, simple laws founded on correct princi- 
ples and expressed in homely language, whereby the navigator 
might quickly develop his position under various conditions at 
sea and along shore. In this little volume has been incorpo- 
rated every practical formula for determining the latitude and 
longitude by dead reckoning and by solar, lunar, and stellar 
observations, as well as concise and lucid directions for chart- 
work, the various sailings, and for accurately fixing the ship's 
place when in sight of land, and in every consideration the 
author has succeeded in simplifying and abridging the confus- 
ing and tedious rules and methods in common use. The purely 
original arrangement of this pocket edition of common-sense 
navigation contributes generously to its value, as it affords means 
of immediate recourse to any and every subject within the 
sphere of the practical navigator. The problems are all worked 
according to Bowditch's American Nautical Tables, which may 
be purchased from any book-dealer for $1.25, but it is to 
be explained that the numbers called for in the text may be 



Vlll PREFACE 

changed to apply to other navigation tables. In no particular 
lias it been attempted to go beyond the limits of honest, service- 
able navigation as practised at* sea, consequently the reader 
would seek in vain for fancy or abstruse sailings and irrelevant 
definitions. 

H. P. 
New York, 1894. 



THE NAVIGATOR'S POCKET-BOOK 



A. M. — Ante Meridiem ; before meridian ; embraces the 
twelve hours from midnight to noon. 

ABOVE THE POLE.— When the north star is situated so 
that it is intercepted between the observer and the pole, it is said 
to be above the pole. This applies to other circumpolar bodies. 
(See Upper Transit.) 

ADJUSTING SCREWS.-(See Sextant.) 

ADJUSTMENT. — The correction of a compass for deviation 
by the employment of magnets, or the regulation of the mirrors 
of a sextant. (See Compass Adjusting ; Sextant.) 

ALIDADE. — An instrument for taking bearings, consisting 
of two arms revolving around a circular brass plate or dial 
marked with the points and degrees of the compass. It is 
secured on top of the binnacle hood and set to the ship's 
course, so that any bearing given by it will represent the mag- 
netic bearing as by the compass beneath. (See Azimuth 
Attachment ; Pelorus.) 

ALMANAC. — A nautical calendar in which is tabulated for 
the various days of the month, the declinations of the sun, 
moon, planets and stars ; their right ascensions ; the equation of 
time, etc. 



2 THE NAVIGATOR'S POCKET-BOOK 

ALTITUDE.— The angular height of a body above the 
horizon. 

Remarks Concerning Meridian Altitudes. — The term me- 
ridian altitude means the highest point attained by a heavenly 
body above the observer's horizon, which is secured when the 
object bears either true north or south as the case may be. 
When the observer is north of the body's declination it will be 
observed to the south, but when the observer is south of the 
body's declination its image will be thrown to the northern 
horizon. 

By mentally adding four minutes of time to the face of the 
ship's clock for every degree of longitude sailed east since the 
clock was last set, or subtracting four minutes for every degree 
sailed west, the observer will be enabled to anticipate the time 
of the meridian passage and be prepared to observe the same. 

There are two methods employed for bringing the image of a 
heavenly body to the horizon at the time of the meridian pas- 
sage, the first of which is as follows : 

Make the vernier and arc zeros cut one another, then, in the 
case of the sun, turn down the shade-glasses to suit the eye ; 
point the telescope toward the body so that its colored image is 
seen in the horizon-glass ; now advance the sliding limb, and in 
proportion as it is moved along the arc, bring the sextant to the 
vertical — otherwise the image would disappear from the horizon- 
glass. 

The second method practised oftentimes at sea for the me- 
ridian observation is to anticipate the approximate altitude 
and to set the same on the sextant, then to direct the telescope 
to that part of the horizon which is beneath the body, making a 
perfect contact by the aid of the tangent screw. This latter 
method obviates the necessity of " shooting the heavens" and 



THE XAVIGATOR S POCKET-BOOK o 

insures against blinding from the dazzling effects of the sun 
•when caught in the unsilvered part of the horizon-glass. To 
calculate the approximate altitude, proceed as follows : 

When the latitude by dead-reckoning and the declination of 
the body are of the same name, subtract them from one another, 
then subtract the remainder from 90° — the answer will be the 
approximate altitude. 

When the latitude by dead-reckoning and the declination of 
the body are of contrary names, add them together, then sub- 
tract their sum from 90° — the answer will be the approximate 
altitude. 

A meridian altitude will always be some part of 90°— an arc 
from the horizon to the point directly over the head of the ob- 
server, called the zenith. This arc is always a quadrant (90°), 
and what an altitude lacks of 90° is always the zenith distance. 

Meridian Altitude of the Sun.— Considering that the sun's 
image has been brought almost in contact with the horizon, 
proceed to make a perfect contact by the aid of the tangent 
screw, fingering the same until the sun's lower limb is just kiss- 
ing the horizon line. The vertical movement of this luminary 
is very slow when approaching the meridian, and within several 
minutes of noon on each side of that point its motion is imper- 
ceptible. Until, however, the body is almost on the observer's 
meridian its limb will show a slow but steady lifting above the 
horizon, and must be brought down when it shows daylight be- 
tween it and that part of the horizon which is directly beneath. 
The idea is to secure the highest altitude which the sun offers. 

In order to be positive of the proper place of contact, the 
navigator should oscillate (swing) the instrument while keeping 
the eye to the telescope, so that the sun's image will appear to 
describe the lower segment of a circle, the lowest point of 



4 THE NAVIGATOR'S POCKET-BOOK 

which will be the horizon directly beneath the sun, and to 
which point the limb of the sun must be brought in contact. 

As soon as it is decided that the sun is done rising, call " eight 
bells ! " The hands of the ship's clock will then be set at twelve, 
as the apparent or sun time at the ship. Although twelve 
o'clock has been " made " at ship, do not consider the observa- 
tion finished until the image of the sun's limb is seen to dip 
below the horizon line ; but when this is observed, under no 
circumstances bring the sun's limb up to the line of the horizon, 
as the dipping of the limb proves that the body has crossed over 
the highest point of the great circle which it describes from 
rising to setting ; and it is from this highest altitude that we 
must calculate the ship's distance from the equator by the appli- 
cation of the declination. 

In relation to the use of the upper and lower limbs of the sun 
when observing its altitude, it will be found that the lower 
limb will afford the most satisfactory result, as a daylight line 
may be distinguished between it and the horizon : whereas the 
sinking of the upper limb to the horizon is attended with danger 
of inaccuracy. (See Latitude.) 

Ex. Meridian Altitude of the Sun. — This altitude is meas- 
ured by simply bringing the sun's image down to that part of the 
horizon line that is directly beneath the body, proving the point 
of contact by the oscillation of the sextant. Without further 
consideration or delay the measured altitude is accepted and read. 

Time Altitude of the Sun. — When observing an altitude of 
the sun for finding the longitude by a chronometer sight or by 
equal altitudes, simply throw the sun's image to that part of the 
horizon which is directly beneath the body, proving the point of 
contact by oscillating the sextant, and at the instant of proper 
contact note the Greenwich hour, minute, and second shown 



THE NAVIGATOR'S POCKET-BOOK 5 

by the chronometer. This may be done by having some one 
stationed by the time-piece, who will make a memorandum of 
the time when so directed by the navigator calling "time" 
when he brings the sun's limb in perfect contact, or it may also 
be done by the navigator himself having a hack watch set to 
Greenwich time which he holds in the hollow of his left hand, 
with its face toward him, so that it is in plain view while 
measuring the altitude. (See Longitude.) 

Altitudes in Foggy Weather. — When, owing to light fog or 
mist, the radius of the visible horizon is only two or three miles, 
get the eye as near to the surface of the water as possible when 
measuring the altitude of a heavenly body, and by this means 
the horizon may often be brought within the fog-described 
circle. Should the fog be heavy, it may be possible to get above 
it by going aloft. When this can be accomplished a good obser- 
vation is obtainable. 

Altitudes in Cloudy Weather. — When the mass of the sun 
or moon is visible, but the limbs ill-defined in consequence of an 
overcast sky or the body shining through a rain-cloud or light 
fog, the image of the mass may be brought down and the centre 
of this ball of light calculated and allowed to be cut by the 
horizon line. In this case no allowance is to be made for 
semi-diameter. The ship's position, determined by this method, 
will probably be a little in error, but as a makeshift the rule has 
its value. 

Meridian Altitude of the Moon. — The astronomical mean 
time of the moon's meridian passage is given in the nautical 
almanac for everyday of the month at Greenwich, and this time 
answers, within a few minutes, for all longitudes. Proceed to 
observe the altitude in the same manner as explained for the sun, 
but use no shade-glasses. If the horns of the moon are down it 



6 THE NAVIGATOR'S POCKET-BOOK 

will be necessary to measure the altitude of the upper limb ; but 
if the horns are up the lower limb will be measured. When the 
moon is full, or nearly so, measure the lower limb always in 
preference to the upper limb. (See Latitude.) 

Time Altitude of the Moon. — This is observed in exactly the 
same manner as described for a time altitude of the sun, omit- 
ting the shade glasses and having regard to the upper and lower 
limbs as explained in Meridian Altitude of the Moon. (See 
Longitude.) 

Meridian Altitude of a Planet. — The astronomical mean 
times of the meridian passages of the planets are given in the 
nautical almanac for every day of the month, and apply prac- 
tically to all longitudes. Proceed in precisely the same way as 
explained for a meridian sight of the sun, but use no shade- 
glasses and do not take the semi-diameter into consideration. 
(See Latitude.) 

Time Altitude of a Planet. — This is observed in exactly the 
same manner as described for a time altitude of the sun, omit- 
ting, of course, the shade-glasses. (See Longitude.) 

Meridian Altitude of a Star. — The following method of ap- 
proximating the star's altitude and placing the same on the sex- 
tant should be observed, as it insures against bringing down the 
wrong body : 

When the latitude by dead-reckoning and the star's declina- 
tion are of the same name, subtract them from one another, then 
subtract the remainder from 90°— the answer will be the rough 
altitude; but when the latitude by dead-reckoning and the 
star's declination are of contrary names, add them together and 
subtract their sum from 90° — the answer will be the rough 
altitude. 

A few minutes before the time given in the star tables (in the 



THE NAVIGATOR'S POCKET-BOOK 7 

back of this volume) for the meridian passage, set the sextant, 
direct it either to the north or south horizons, according to the 
latitude of the ship and the declination of the body, and the 
star's image will be seen in the horizon-glass of the instrument ; 
then make a perfect contact by the aid of the tangent screw, and 
wait for the star to reach its highest point, proceeding in the 
same manner as described for a meridian observation of the sun, 
it being understood that shade-glasses are not employed. 

The declination of the star as compared with the latitude of 
the ship will always dictate the direction (north or south) in 
which to look for the horizon beneath the body. If the star's 
declination is north of the ship's position, the northern horizon 
will be used, but if the star's declination is south of the ship's 
position, the southern horizon will be used. 

Dawn and twilight afford the best horizons for star observa- 
tions. (See Latitude.) 

Time Altitude of a Star. — This is observed in the same man- 
ner as described for a time altitude of the sun, only without 
making use of the shade-glasses. It is to be explained, how- 
ever, that until the navigator has studied the heavens and be- 
come sufficiently familiar with them to locate the nautical stars 
when they are off the meridian, this method of finding the 
longitude cannot be employed by him. The superior size and 
brilliancy of the planets will always prove an unfailing guide 
when desiring to select one of those bodies, but confusion will 
at once arise in seeking to fix upon particular stars unless the 
observer is acquainted with their relative places. (See Fixed 
Stars ; Longitude.) 

Altitude of the Pole Star.— Simply throw the star's image to 
that part of the horizon which is directly beneath the body, 
proving the point of contact by oscillating the sextant, and note 



8 THE NAVIGATOR'S POCKET-BOOK 

the local apparent time at ship as shown by the clock. (See 
Latitude.) 

Remarks. — Under the head of Sextant will be found full and 
practical directions for adjusting the instrument and reading 
the altitude. (See also Corrected Altitude ; Quadrant ; Oc- 
tant.) 

If the star telescope is used, be particular to observe as closely 
as possible in the centre of the field. 

AMPLITUDE.— The bearing (never exceeding 90°) of a 
heavenly body at rising or setting. To ascertain the variation 
and deviation of a compass by employing an amplitude, pro- 
ceed as follows : 

To Find the Magnetic Amplitude. — Observe the sun to 
rise or set and note its magnetic bearing by the compass, pelorus, 
or alidade, which bearing will be named east so many degrees 
north or south at rising, but west so many degrees north or 
south at setting, as the case may be. 

To Find the True Amplitude.— With the latitude by dead- 
reckoning to the nearest degree, and the sun's declination to the 
nearest half degree, enter table 39 and select the sun's true bear- 
ing, which will be named north if the declination is north, and 
south if the declination is south. 

To Find the Whole Variation. — The difference between the 
compass bearing and the true bearing (subtracted if of the same 
name, but added if of different names) will be the whole amount 
of the compass variation, or the angle made with the true me- 
ridian by the compass needle, and it will be named as follows : 

To Name the Variation. — Refer to a compass card and mark 
the points representing the bearings, then imagine the eye in 
the centre of the compass looking at the point standing for the 
magnetic (compass) bearing, and if the true bearing is to the 



THE NAVIGATOR'S POCKET-BOOK 9 

right hand of the magnetic bearing the variation is easterly, 
but if to the left hand it is westerly. 

To Find the Deviation. — If the compass has no deviation, 
then the whole amount of the variation determined by the am- 
plitude will agree with the variation given by the chart for the 
ship's position, but if they do not agree, their difference will be 
the deviation of the compass for that particular course the ship 
was heading at the time of the observation, and it will be named 
according to the following : 

To Name the Deviation. — Suppose that the variation found 
by amplitude is 10° east, and the variation given by the chart is 
5° west. Now as the chart tells us that the north point of our 
compass needle in order to be correct magnetic should be in- 
clined 5° to the west of the geographical or true north, and we 
find by our observation that it is inclined 10° to the east, it stands 
that the compass has 15° of easterly deviation. 

Again, suppose the variation found by amplitude is 8° east, 
and the variation given by chart is 3° east, it shows that the com- 
pass needle is deflected 5° too much to the east, hence easterly 
deviation. 

Once more, suppose that the variation found by amplitude is 
15° west and the variation given by chart is 13° west ; it shows 
that the compass needle has 2° of westerly deviation. 

AMPLITUDE TABLES.— True bearings of heavenly bodies 
at rising and setting, calculated for various latitudes and dec- 
linations. 

ANEMOMETER. — An instrument that measures the force 
of the wind. 

ANEROID BAROMETER. — An instrument that registers 
atmospheric pressure, its principle of construction being as fol- 



10 THE NAVIGATOR'S POCKET-BOOK 

lows : The weight of the atmosphere presses on a thin metal 
box from which the air has been extracted and which is kept 
from collapsing by a spring. To this box is secured by a me- 
chanical arrangement the index-hand that moves around the dial 
or face of the barometer. When the atmospheric pressure in- 
creases a spring, acting on a lever, turns the hand to the right, 
and when the pressure decreases the hand turns to the left. (See 
Barometer.) 

ANGLE.— The divergence of two lines starting from the 
same point. (See Angle of Incidence.) 

ANGULAR DISTANCE.— Measured by an angle ; a certain 
number of degrees of arc. 

ANNUAL VARIATION.— The yearly change of the com- 
pass variation in the same locality, or the yearly change of dec- 
lination and right ascension tabulated for the fixed stars. 

ANTARCTIC CIRCLE.— The parallel of 66° 32', which di- 
vides the south temperate from the south frigid zone. 

APPARENT TIME.— Time calculated by the sun. When 
the sun crosses the meridian of the observer it is apparent noon 
where he is, as well as at all places on his meridian from pole to 
pole. 

ARC. — A part of a circle. (See Diurnal Arc ; Nocturnal Arc ; 
Sextant.) 

ARCTIC CIRCLE,— The parallel of 66° 32', which divides 
the north temperate from the north frigid zone. 

ARITHMETIC OF NAVIGATION.— The arithmetic of 
practical navigation is extremely simple and is included in the 
following: 



THE NAVIGATOR'S POCKET-BOOK 11 

Angular Measure. — 

60 seconds (60") make 1 minute (1'). 
60 minutes (60') make 1 degree (1°). 
Time Measure. — 

60 seconds (60 sec.) make 1 minute (1 m.). 
60 minutes (60 m.) make 1 hour (1 h.). 
To Convert Time into Arc. — Convert hours, minutes, and 
seconds into arc according to table 7 or by the following : 
1 hour is equal to 15°, so multiply the hours by 15. 
4 m. is equal to 1°, so divide the minutes by 4. 
4 sec. is equal to 1', so divide the seconds by 4. 
To Convert Arc into Time. — Multiply the longitude by 4 
and this will turn the degrees of arc into minutes of time, the 
minutes of arc into seconds of time, and the seconds of arc into 
what is known as thirds of time (a third is the name given to 
the sixtieth part of a second). By dividing by 60 these quanti- 
ties will be reduced to hours, minutes, and seconds of time. 
(See table 7.) 

Arithmetical Signs. — 

== equal to, the sign of equality. 
H- plus, the sign of addition. 
— minus, the sign of subtraction. 
x multiplied by, the sign of multiplication. 
-f- divided by, the sign of division. 
Addition of Degrees, Minutes, and Seconds. — 
35° 30' 20" 27° 27' 56" 

20° 20' 30 " 36° 57' 49 " 

55° 50' 50" 64° 25' 45" 

Subtraction of Degrees, Minutes, and Seconds. — 
11° 12' 10" 26° 35' 42" 

10° 10' 10" 12° 45' 50" 

1° 02' 00" 13° 49' 52" 



12 THE NAVIGATOR'S POCKET-BOOK 

Multiplication of Degrees, Minutes, and Seconds. — 

10° 10' 10" 13° 59' 58" 

_5 3 

50° 50' 50" 41° 59' 54" 

Division of Degrees, Minutes, and Seconds. — 

2)40° 20' 10" 2)37° 15' 52" 



20° 10' 05" 


18° 37' 56 


Addition of Decimals. — 




6.5 


7.9 


5.2 


6.9 


3.2 


4.9 


14.9 


19.7 


Subtraction of Decimals. — 




19.7 


29.5 


4.3 


13.6 


15.4 


15.9 


Multiplication of Decimals. — 




20.1 


15.6 


5 


4 


100.5 


62.4 


Division of Decimals. — 




2)18.4 


2)17.6 


9.2 


8.8 



ARTIFICIAL HORIZON.— A small trough rilled wilh 
quicksilver, which latter is protected from the ruffling effects 
of the wind by a glass roof. It is used on shore to catch the 
image of a heavenly body and to measure its altitude for the 4 
purpose of determining the latitude and longitude. A pan of 



THE NAVIGATOR'S POCKET-BOOK 13 

molasses or liquid tar has often been employed with fairly good 
results, in the absence of a regular artificial horizon. 

The theory of the artificial horizon is based upon the estab- 
lished principle that the angle of reflection is equal to the angle 
of incidence — that a ray of light striking a plane-reflecting sur- 
face will leave it at the same angle precisely. 

Rules. — Place the trough on firm ground and as free from the 
wind as possible so that the surface of the liquid may not be 
disturbed, then face the heavenly body and step backward until 
its reflection is seen in the quicksilver. The image will now be 
brought down by the sextant until it is in contact with the other 
image in the trough, and the angle shown on the sextant will be 
double the altitude of the body, consequently it will be divided 
by 2. 

When observing the lower limb of the sun in the morning the 
images will separate, but in the afternoon they will close. 

In the case of the sun, if the nearest limbs of the two images 
are brought in contact half of the angle obtained by the sextant 
will be the altitude of the lower limb, but if the farthest limbs 
are brought in contact half of the angle obtained will be the 
altitude of the upper limb, and the semi-diameter will be applied 
according to the regular rules given for the sun under the head 
of Corrected Altitude. The sun's altitude obtained must also 
be corrected for parallax and refraction, but not for dip, because 
that quantity is eliminated by the use of the artificial horizon. 

When ready to observe the altitude for a time sight it is best 
to separate the images or overlap them a trifle, as the case may 
require ; then wait, in the first place, for them to kiss (close), or, 
in the second place, for the limbs to all but part, and at such 
instant of perfect contact note the Greenwich time and proceed 
to find the place of the observer by the given rules. 



14 THE NAVIGATOR'S POCKET-BOOK 

Before observing an altitude the glass roof should be carefully 
wiped clean, and if dust-scum is seen to rest on the surface of 
the mercury it should be brushed off. 

"When equal altitudes are observed be sure to measure the same 
limb in the p.m. that was measured in the a.m.; otherwise the 
result will be unsatisfactory. 

It is to be explained that when a heavenly body is much more 
than 60° above the horizon it cannot, as a rule, be measured by 
an artificial horizon, because on the majority of sextants the 
reading does not go far above 120°. 

ASTRONOMICAL DAY.— This commences at noon of the 
civil day, the hours being counted numerically from 1 to 24, so 
that the day begins and ends at noon. 

ASTRONOMICAL TIME.— The civil day begins at mid- 
night, twelve hours before the astronomical day, which com- 
mences at noon. To convert civil time into astronomical time 
it is only necessary to proceed as follows : 

If the civil time is a.m. take one from the date and add 12 to 
the hours ; but if the civil time is p.m. simply take away the 
sign p.m., and the answer will be. the astronomical time. 

To change astronomical time into civil time, if the hours are 
less than twelve, simply write p.m. after them ; but if the hours 
are more than twelve subtract twelve hours from them, call the 
remainder a.m., and add 1 to the days of the month. 

ASTRONOMY.— That science which treats of the heavenly 
bodies, their orbits, distances, etc. 

AUGMENTED ALTITUDE.— Increased altitude ; the cor- 
rection in arc added to an ex-meridian altitude. 

AUTUMNAL EQUINOX.— The period of the year when 
the sun crosses the equator from northern into southern declina 



THE NAVIGATOK'S POCKET-BOOK 15 

tions. This is known as the First Point of Libra. (See Spring 
Equinox.) 

AXIS. — A line on which a body is supposed to revolve. 

AXIS OF COLLIMATION.— The line of sight in an instru- 
ment, being the line which passes through the centre of the 
object-glass and the intersection of the wires placed in its focus. 
What is known as the error of collimation is the difference 
between the actual line of sight and the position which that line 
should have in reference to the axis of motion of the instrument. 
Should the line of sight of the telescope be inclined to the plane 
of the instrument, instead of perfectly parallel to it, all angles 
measured by the sextant will be too great, 

AZIMUTH.— The bearing (never exceeding 180 c ) of a heav- 
enly body calculated from the north or south points of the 
heavens. To ascertain the variation and deviation of the com- 
pass by an azimuth, proceed as follows : 

To Find the Magnetic Azimuth and Time. — Observe the 
sun's bearing by compass, alidade, or pelorus, and note the local 
time shown by the ship's clock, which latter correct by adding 
to it four minutes of time for every degree of longitude sailed 
east since the clock was last set, but by subtracting four min- 
utes for every degree sailed west. 

In north latitudes a.m. azimuth bearings are counted north so 
many degrees east, and p.m. azimuth bearings are counted north 
so many degrees west. 

In south latitudes a.m. azimuth bearings are counted south so 
many degrees east, and p.m. azimuth bearings are counted south 
so many degrees west. 

To Find the True Azimuth. — With the corrected local ap- 
parent time and the latitude of the ship to the nearest degree 



16 THE NAVIGATOR'S POCKET-BOOK 

by dead-reckoning, also the declination of the sun to the nearest 
degree, enter the azimuth tables and select the sun's true bearing. 

To Find the Whole Variation. — The difference between the 
compass and true bearings (always found by subtracting one 
from the other) will be the whole amount of the variation of 
the compass needle from the true north, and it will be named as 
follows : 

To Name the Variation. — Refer to a compass card and mark 
the two points representing the bearings, then imagine the eye 
in the centre of the compass looking at the point standing for 
the magnetic (compass) bearing, and if the true bearing is to the 
right hand of the magnetic bearing the variation is easterly, but 
if to the left hand, it is westerly. 

To Find the Deviation. — If the compass has no deviation, 
then the whole amount of the variation determined by the azi- 
muth will agree with the variation given by the chart for the 
ship's position, but if they do not agree their difference will be 
the deviation of the compass for that particular course headed 
by the ship at the time of the observation, and it will be named 
according to the following : 

To Name the Deviation. — Suppose that the variation found 
by azimuth is 7° west and the variation given by chart is 9° east. 
ISfow as the chart tells us that the north point of our compass 
needle in order to point correct magnetic should be inclined 9° 
to the east of the geographical or true north, and we find by our 
observation that it is inclined 7° to the west, it stands that the 
compass has 16° of westerly deviation. 

Again, suppose that the variation found by azimuth is 14° 
west and the variation given by chart is 6° west : it shows that 
the compass needle is deflected 8° too much to the w T est, hence 
westerly deviation. 



THE NAVIGATOR'S POCKET-BOOK 17 

Once more, suppose that the variation found by azimuth is 
20° east and the variation given by the chart is 19° east : it 
proves that the compass needle has 1° of easterly deviation. 

AZIMUTH ATTACHMENT.— A small, portable, mechani- 
cal device, consisting of two revolving arms or sight-vanes, for 
resting on the compass-glass and by which bearings are taken. 
(See Alidade ; Pelorus.) 

AZIMUTH CIRCLE.— Another name for an azimuth at- 
tachment. 

AZIMUTH COMPASS.— A portable, dry -card compass 
provided with sight- vanes and used for taking bearings. It is 
now obsolete. 

AZIMUTH MIRROR.— A small, portable instrument pro- 
vided with a silvered glass and used for taking bearings. It 
steps in a small, shallow hole bored in the centre of the com- 
pass-glass, and is turned around until the image of the desired 
object is seen in the mirror, when its bearing is read. (See Ali- 
dade ; Azimuth Attachment ; Pelorus.) 

AZIMUTH TABLES.— True bearings of the sun calculated 
for various latitudes, declinations, and times from sunrise to 
sunset. 

BACK SHADES.— (See Sextant.) 

BAROMETER. — An instrument for measuring the weight 
or pressure of the atmosphere, and sometimes referred to as a 
weather-glass, as it indicates the probable changes in the weather. 
The normal condition or average standing of the barometer for 
the sea-level is about thirty inches. As a rule, when the barom- 
eter continues steady, settled weather may be anticipated ; but 
if it is unsteady, a change is promised. A sudden rise of the 
2 



18 THE NAVIGATOR'S POCKET-BOOK 

barometer is nearly as bad as a sudden fall, as it proves that the 
equilibrium of the atmosphere is unsettled. The average range 
(rise and fall) of the barometer in the higher latitudes is 1.5 (one 
inch and five-tenths) ; in the intertropical parallels from 0.2 to 
0.4 (two to four-tenths), and near the equator only 0.15 (fifteen- 
hundred ths of an inch). In hurricanes the barometer ranges 
from 1.0 to 2.5 (one to two and a half inches) — the rapidity of 
the fall increasing as the storm-centre approaches. 

On the mercurial barometer the scale is spaced off in inches, 
whence is derived such terms as " the barometer staudsat thirty 
inches/' etc., meaniDg in this instance that the level of the mer- 
cury in the glass tube is opposite the thirty-inch division of the 
scale. (See Aneroid Barometer ; Mercurial Barometer ; Law of 
Storms; Weather.) 

BASE-LINE. — The lowest side of a geometrical figure ; at 
a right angle to the perpendicular. 

BEARING. — The direction of one object from another ac- 
cording to the compass. (See Alidade ; Azimuth Attachment ; 
Pelorus.) 

BELOW THE POLE. — When the north star is situated so 
that the pole is intercepted between it and the observer, it is said 
to be below the pole. This applies to other circumpolar bodies. 
(See Latitude ; Upper Transit.) 

BOXING THE COMPASS.— (See Compass.) 

CARDINAL POINTS.— North, East, South, and West. (See 
Intercardinal Points.) 

CELESTIAL.— Relating to the heavens. 

CELESTIAL CONCAVE.— The heavens. 

CHART.— A marine map showing coasts, shoals, etc., etc. 



THE NAVIGATOR'S POCKET-BOOK 19 

All charts are projected true (parallels and meridians geographi- 
cal), but the compass diagrams printed on them may be either 
true or magnetic, as described under the head of Chart Sailing. 
The parallels are represented by straight lines drawn true east 
and west across the chart, and the meridians by straight lines 
drawn true north and south. If the degrees and minutes marked 
on the right and left hand margins of the chart increase upward, 
the chart represents north latitudes, but if they decrease upward 
the chart represents south latitudes. If the degrees and minutes 
marked on the top and bottom margins of the chart increase 
toward the right hand, the chart represents east longitudes, but 
if they decrease toward the right hand the chart represents west 
longitudes. Charts are drawn on a large scale or a small scale 
according to the extent of ocean or coast to be delineated, and it 
is to be understood that buoyage, lights, soundings, etc., are 
fully explained on the charts representing the waters they refer 
to, and such explanations and directions as are given apply 
especially to that particular chart on which the details are read. 

Buoys are marked B. (black), Cheq. (chequered), H. S. (hori- 
zontal stripes), R (reel), W. (white), B. W. (black and white), 
B. R. (black and red), R. W. (red and white), V. S. (vertical 
stripes). Buoys painted with black and white perpendicular 
stripes mark a mid-channel and must be passed close to to avoid 
danger. A green buoy marks a wreck. Perches with balls, 
cages, etc., mark turning-points in the channel. On the coast 
of the United States, when approaching a channel from seaward, 
red buoys with even numbers are left on the starboard side, and 
black buoys with odd numbers are left on the port side. Buoys 
painted with red and black horizontal stripes indicate obstruc- 
tions with channel -ways on either side. 

The quality of the bottom is expressed in abbreviations, as 



20 THE KAVIGATOK'S POCKET-BOOK 

follows : blk. (black), b. (blue), bkn. (broken), br. (brown), cl. 
(clay), co. (coarse), crl. (coral), d. (dark), f. (fine), gy. (gray), g. 
(gravel), gn. (green), grd. (ground), h. (hard), m. (mud), oz. 
(ooze), oys. (oysters), peb. (pebbles), rd. (red), r. (rock), rot. 
(rotten), s. (sand), sli. (shells), sft. (soft), spk. (speckled), stf. 
(stiff), st. (stones), wd. (weed), w. (white), y. (yellow). 

Soundings, unless otherwise specified, are indicated according 
to the following : The numerals marked on the white surfaces 
represent the depth of the water at that point in fathoms (six 
feet), and when marked on the dotted surfaces they indicate the 
depth in feet (12 inches). All soundings are given for mean 
low water, and the rise of the tide at the given place is to be 
added to the sounding to ascertain the greatest depth of water 
at high tide at that particular point. 

During fog or falling snow, vessels approaching light-ships 
will be warned by the alternate ringing of a bell and the blow- 
ing of a fog-horn. 

Lights are shown by a dot of yellow having a red spot in the 
middle, and if any uncertainty exists concerning the character 
of a light it is simply marked Lt. Other abbreviations and 
their significance are as follows : F. (fixed), Fl. (flashing), Int. 
(intermittent), Eev. (revolving), F. and Fl. (fixed and flashing 
alternately), Fig. (floating), Lt. Yes. (light-vessel). When no 
color is expressed the light may be taken to be white. When- 
ever the color is given the word is spelled in full, as red, etc. 

Currents are shown by a feathered arrow; the direction of the 
same indicating the flow of the current. Flood- tide stream is 
indicated by an arrow feathered on one side only, and ebb-tide 
stream by an unfeathered arrow. 

Rocks just below the surface of the water are shown by a 
small dotted circle having a cross in the centre. Rocks awash 



THE NAVIGATOR'S POCKET-BOOK 21 

or just above water are shown by a dotted circle with one or 
more dots inclosed according to the number or extent of the 
rocks indicated. A dotted circle with a numeral in it signifies 
a shoal with the number of feet or fathoms over it. Either a 
rock, an island, or a shoal marked E. D. signifies existence 
doubtful, and if marked P. D., it means position doubtful, al- 
though known to exist. (See Pricking Position.) 

Mercator's Chart. — This is the chart universally adopted as 
the only proper chart for general navigation. The parallels 
and meridians are all straight parallel lines, but the meridians 
only are equidistant. The distance between the parallels in- 
creases from the equator toward the poles in proportion as the 
meridians converge. This chart projection is constructed by 
the aid of the table of meridional parts and the rule given in 
Bow ditch. 

On the surface of the globe the parallels of latitude are every- 
where equidistant, while the distance between the meridians 
lessens as we proceed polar wise. Thus it will be appreciated 
that if on a plane chart the parallels are retained equidistant 
while the meridians are widened out in order to show them as 
straight lines and as far apart in the vicinity of the poles as 
they are at the equator, there must be considerable distortion in 
one direction — namely, the longitude. This difficulty of de- 
lineation may be surmounted and the relation between the 
principal parts maintained by also distorting the chart polarwise 
or in a north and south direction; consequently the distance be- 
tween the parallels is widened in the same proportion that the 
meridians have been widened. Of course this will distort the 
land and sea more and more in the parallels approaching 
the poles, but as the scale on the right and left hand margins of 
the chart allows for this, and as the contour of the countries is 



22 THE navigator's pocket-book 

preserved, as well as the relative directions from one point to 
another, no inconvenience is experienced by the navigator. 
(See Chart Sailing.) 

Chart of the Inclination. — A chart which shows the dip of 
the magnetic needle for various latitudes and longitudes. 

Coast Survey Chart. — A chart of the coast published by 
Government. 

General Chart. — A chart embracing a large expanse of ocean 
or extent of coast. 

Harbor Chart. — A chart, as its name implies, which de- 
lineates a harbor. 

It is a detached portion of a general chart and is shown on a 
large scale. As a rule the parallels and meridians are not 
shown on harbor charts, and the scale is given in miles. 

Physical Chart. — A chart showing ocean currents, winds, 
ice limits, etc. 

Great Circle Chart. — A chart constructed specially so that 
all great circles are represented as straight lines. This answers 
the same purpose for great-circle sailing that Mercator's chart 
answers for rhumb-sailing. The construction of the great-circle 
chart is such that a straight line drawn on it connecting the 
place of departure with the place of destination gives imme- 
diately the great-circle track. 

Hydrographic Charts. — Charts published by the Washington 
Hydrographic Office, which delineate the navigable waters of 
the world, rocks, shoals, tides, currents, depths, etc., and give 
the varied information in a convenient form for the navigator. 
The surveys are made by American naval officers and the charts 
are published by the United States Government. 

Variation Chart. — A chart of the world on Mercator's pro- 
jection, on which is represented the variation of the compass in 



THE NAVIGATOR'S POCKET-BOOK 23 

different latitudes and longitudes by a series of curved lines ; 
also known as an isogonic chart. 

CHART SAILING. — This ebmraces several considerations, 
which will be taken up in order. 

To Shape the Course.— Place the same bevelled edge of the 
parallel rules over the ship's place and the point bound to ; then, 
preserving the angle, slide the edge to the nearest compass dia- 
gram printed on the chart until it lies on the dot in the centre ; 
now read the compass-point looking toward the place sought, 
and that will be the required course. (See Course Protractor ; 
Graduated Rulers.) 

In case the distance between the two places is too great to be 
reached by the parallel rules, take a piece of string and stretch 
it from one point to the other by the aid of pins stuck in the 
chart through the two places ; then lay the bevelled edge of the 
rule against the string to obtain the angle, and proceed as before 
explained. 

To Allow for Variation. — On some charts the north and 
south line of the diagram compass is parallel with the meridian 
line, while on other charts the north and south line of the dia- 
gram compass forms an angle with the meridian line. In the 
latter case it proves that the diagram indicates magnetic direc- 
tions ; consequently the course found by the parallel rules will 
be steered (unless deviation exists), as the diagram on the chart 
is a reflection of the compass on board the vessel. On the other 
hand, where the north and south line of the diagram compass 
is parallel with the meridian, it proves that the diagram indi- 
cates true or geographical directions. In this case it becomes 
necessary to allow for the variation of the compass as fol- 
lows : 

Example. — Suppose that the course found by a true compass 



24 THE navigator's pocket-book 

diagram is north and the chart tells us that where the ship is 
situated there is one point of westerly variation, which means 
that the north end of the compass needle is inclined one point 
to the west of the true or geographical noith. Under these 
circumstances, it will be necessary to steer north-by-east by the 
ship's compass in order to make a true north course. 

Note. — A simple rule to remember for converting true courses 
into magnetic courses is to allow the amount of westerly varia- 
tion away from the true course in the direction that the Jiands 
of a watch revolve, and easterly variation contrary, or against 
the hands of a watch. 

To Allow for Deviation. — If deviation exists for the correct 
magnetic course found, then the correct magnetic course must 
have the amount of the deviation applied to it on exactly the 
same principle as explained for variation in the preceding para- 
graph. 

Example. — The correct magnetic course is east and there is 
one point of westerly deviation to be allowed when the ship's 
head is on that course ; consequently the compass course to be 
steered is east-by-south in order to make a correct magnetic east 
course. 

Always apply the variation before applying the deviation. 

To Measure the Distance. — Contain between the points of 
the dividers the position of the ship and the port bound to, then 
apply this span to the graduated meridian (side margin or bor- 
der) of the chart directly opposite the latitudes you are to sail in, 
and read the distance indicated. 

If the span is too great to be contained between the points of 
the dividers, then set the latter to any convenient number of 
miles or degrees by the scale on the side of the chart opposite the 
latitudes the ship is to traverse, and ascertain the number of 



THE ^AYIGATOK'S POCKET-BOOK 25 

times that this " set" is contained on the direct line of the ship's 
course, and so calculate the distance. 

The reason for setting the dividers to the scale opposite the 
parallels to be sailed in is on account of that particular scale 
belonging to those parallels. As explained under the head of 
Charts, the distance between the parallels increases from the 
equator toward the poles, consequently the scale given for the 
parallels near the equator will not answer for higher latitudes. 

The two graduated parallels (top and bottom margins on bor- 
ders) on the chart are marked in degrees and minutes, but on 
these parallels longitude-in-arc is measured, nothing more ; dis- 
tance cannot be taken from them, and they are only employed 
for laying off the longitude. 

Cross-Bearings. — Observe in quick succession the compass- 
bearings of two lights (or other stationary objects which are 
defined on the chart), then refer to the chart, and by the aid of 
the parallel rules and the magnetic diagram compass draw pencil 
lines along the paper from the lights in question, according to 
the respective bearings of the two objects, and the point where 
the lines cross will show the position of the ship at the time the 
bearings were taken. 

Remarks. — It is to be understood that the compass bearings 
are to be corrected for the deviation (if any exists) of the ship's 
head at the time the bearings were taken, so as to convert them 
into correct magnetic bearings before applying the lines to the 
chart. 

It must be remembered that if the chart is provided with true, 
instead of magnetic compass diagrams, the variation of the com- 
pass must also be applied to the respective bearings in order to 
convert them into true bearings ; then these latter must be trans- 
ferred to the chart, plotting them from the true compass diagram. 



26 THE navigator's pocket-book 

Vertical Danger Angle. — The danger angle Las, to a great 
extent, taken the place of cross-bearings for locating the posi- 
tion of a vessel when in sight of lighthouses, either by day or 
night. It is extremely easy of solution, and by the aid of the 
danger-angle tables to be found in the back of this little volume 
the navigator will discover it to be a very simple matter, both to 
fix the position of his ship and to keep outside of dangers in the 
way of rocks and shoals situated at a distance from the shore. 
(See Danger-xAngle Tables.) 

First Consideration. — To determine the place of the ship, 
take a compass-bearing of any lighthouse in sight ; the vessel 
will be somewhere on this line of bearing. Then with the 
sextant measure the altitude of the light by throwing the reflec- 
tion of the lantern to the water line. By consulting the danger- 
angle tables with the measured angle and the height of the light 
above the sea-level (the latter is given on the chart) the distance 
of the vessel seawards from the light will be read in the side 
column to the left. 

Second Consideration. — To explain another practical applica- 
tion of the vertical danger angle, let it be supposed that a ves- 
sel is forced to closely round a lighthouse, at some distance 
seawards of which there is a cluster of rocks a few feet under 
water. Now with the dividers measure the distance from the 
light to a point well outside of the danger, then with this dis- 
tance and the height of the light enter the danger-angle tables 
and read the angle given. Place this angle on the sextant and 
when approaching and passing the light observe that this angle 
does not increase, otherwise the ship will be inside the danger 
mark. If the angle decreases the ship will be farther outside 
the danger mark than there is necessity 7 for. 

Remarks. — In measuring vertical danger angles, when the 



THE NAVIGATOR'S POCKET-BOOK 27 

lighthouse is comparatively close, the observer should get as 
near to the surface of the water as the deck will admit in order 
to reduce the error arising from the eye being elevated above 
the sea -level. It is to be explained, however, that if this 
point is disregarded altogether, the slight error will lie on the 
safe side, so long as there exists no danger seawards of the 
ship. 

If the sextant has an index-error the same must be allowed 
for in measuring danger angles. (See Sextant.) 

Horizontal Danger Angle. — Where the vertical danger angle 
is dependent upon a lighthouse, the height of which is known, 
the horizontal danger angle may not only be worked by two 
lighthouses independent of their height, bnt in the daytime it 
may be employed by using any two well-defined objects on 
shore, such, for instance, as prominent features of the coast-line, 
buildings, etc. In the horizontal danger angle no tables are 
used, the navigator calculating his own angle. 

We will suppose that the chart shows a number of rocks or 
shoals stretching for some little distance along the coast, and 
that back of them on the shore are a life-saving station and a 
church. Sweep the smallest circle with a pencil point dividers 
that will pass through the two shore objects and inclose all the 
dangerous features between them. Now from a seawards point 
on this circle, draw lines to the two objects on shore so that the 
lines will look like the plotting of a cross-bearing. The respect- 
ive directions of these two lines will be measured by the parallel 
rules and the nearest chart compass, and the angle shown by the 
divergence of the lines will be turned into degrees. This angle 
will be placed on the sextant, and when approaching and pass- 
ing the danger the navigator will observe that the angle does 
not increase, otherwise he will know that he is inside the danger 



28 the navigator's pocket-book 

line. If the angle decreases it is a sign that he is outside or sea- 
wards of the danger line. 

As its name implies, this angle is measured by holding the 
sextant horizontal and sweeping one object into the other. 

It matters not from what seawards point of the circumference 
of this circle the angle is measured — it will give the same re- 
sult ; consequently by steering the ship so as to preserve the 
given angle, the navigator would sail right around the circle 
drawn by the pencil-point dividers. 

Example. — We will suppose that off a section of the coast 
defined by two headlands, several clusters of rock are shown to 
extend between them and to lie off shore at a distance of two 
miles. Our course being close along the coast it is necessary to 
take precautions in approaching and passing this dangerous 
point. 

By the aid of a pencil-point dividers (or a small piece of lead- 
pencil fastened to one leg of the common dividers) we sweep a 
circle which passes through the headlands and incloses every 
part of the shoal. Next we draw two pencil lines from a sea- 
wards point on this circle so that they will pass through each 
headland ; then we ^determine their respective bearings by the 
parallel rules and the chart compass. 

One headland, we will say, we find to bear north -northeast, 
and the other northwest. These bearings equal six compass- 
points, or 67°; consequently this is the horizontal danger angle, 
and we place the same on the sextant and observe that it does 
not increase as we approach and pass the shoal. 

Four-Point Bearing. — This is an extremely simple and use- 
ful problem. When approaching a lighthouse, light-vessel, or 
a point of land, note its compass-bearing when it is four points 
on the bow. When the object is exactly abeam calculate the 



THE NAVIGATOR'S POCKET-BOOK 29 

distance run from the time the first bearing was taken, and this 
will be the distance of the ship from the light abeam. 

Example. — A ship is steering north, making ten knots per 
hour. At 7 o'clock a lighthouse bears northwest, and at 7.30 
o'clock it bears west, or directly abeam. The distance run in 
the interval is five miles ; consequently the ship is five miles east 
of the light. 

Remarks. — The ship is not supposed to change her course in 
the interval between bearings. 

In this problem the deviation of the compass is not considered, 
as the vessel maintains the same course ; consequently, the devia- 
tion being the same for both bearings, it is ignored. 

An object to bear directly abeam must subtend an angle of 
eight points of the compass, or 90°, to the ship's course ; for ex- 
ample, if a ship is steering northwest, an object will be directly 
abeam on the port side when it bears southwest, and directly 
abeam on the starboard side when it bears northeast. 

Patterson's Method. — This conception of the author's affords 
the means of locating the vessel by two compass-bearings of the 
same object when in sight of land, where only a single light, 
headland, or other fixed feature is to be seen. 

Rule. — Observe the bearing of the object and note the time. 
After holding the course until the object has changed its bearing 
at least two or three points, note again its bearing and the time, 
and calculate the distance the vessel has run in the interval be- 
tween the first and last bearings. Trace the two lines of bear- 
ing on the chart in pencil, then span the dividers to the distance 
run, and proceed as follows : 

With the parallel rules set to the course sailed by the ship be- 
tween bearings, move them along the pencil lines until both 
points of the dividers, held against the bevelled edge of the rules, 



30 THE NAVIGATOR'S POCKET-BOOK 

just fit across the lines, and these two points where the dividers 
rest w T ill show the position of the vessel at the time of the first 
hearing as well as her place at the time of the second bearing. 

Remarks. — The two compass-bearings must be corrected for 
the deviation (if any exists) of the ship's head at the time the 
bearings were taken, so as to convert them into correct magnetic 
bearings before tracing them on the chart. 

The compass course must also have the deviation applied to 
it so as to reduce it to a correct magnetic course before setting 
the parallel rules by the diagram compass on the chart. 

CHIP LOG —This log can claim at least one advantage over 
the patent log, inasmuch as the vessel's rate of speed can be de- 
termined by it at any given instant, whereas the patent log is 
useful only for recording a considerable distance run. 

The log line should be about one hundred and fifty fathoms 
long and marked off in knots, the distance between which should 
stand for the same part of a sea mile as the 30 seconds sand- 
glass stands for an hour — namely, the 120th part — which would 
make the lengths between the knots about fifty-one feet. When 
a 28 seconds glass is used the length between the knots should 
be about forty-seven feet. 

It has been found, however, from practical experience, that 
the chip log records somewhat less than it should owing to the 
log coming home after being hove. To compensate for this, 
navigators should shorten the distance between the knots so that 
for a 30 seconds glass they should be forty-eight feet apart, and 
for a 28 seconds glass, forty-five feet apart. 

Heaving the Log.— One man holds the reel and another the 
sand-glass. The officer throws the log chip over the ship's stern, 
and when he observes that the stray line is run off (about ten fath- 
oms—this distance being allowed to carry the log out of the in- 



THE NAVIGATOR'S POCKET-BOOK 31 

fluence of the ship's wake), he calls " turn ; " the seaman upsets 
the glass and watches until the sand is run out, then calls " stop." 
The officer stops the line by a sudden jerk which pulls the plug 
out of its hole in the chip and so allows the log to float horizon- 
tal, then observes the number of marks that have passed over the 
tafirail. The last mark shown indicates the knots, and the dis- 
tance of the mark outside of the tanrail shows the fractions of 
the knot estimated in eighths (eight furlongs to the mile). The 
knots and furlongs give the speed of the vessel in nautical miles 
or knots. 

Remarks. — When running before a heavy sea, allowance 
must be made, for the ship will make greater speed than indi- 
cated by the log. Under such conditions it is customary to add 
one mile for every ten knots run out. 

Driving against a heavy sea it is the rule to subtract one mile 
for every ten knots run out. 

In heaving the log, the line must be helped from the reel by 
the officer, so that no strain is brought upon the chip as it rests 
in a perpendicular position in the water ; otherwise the wooden 
peg which forms a part of the bridle will pull out and the log 
will lie flat on the surface. 

The line must be measured occasionally, and if it is found to 
be stretched, it must be carefully remarked, otherwise it will 
prove deceptive. 

Compare the sand-glass at times with a watch to see that it runs 
out in the prescribed number of seconds. 

The glass is more or less influenced by the weather, running 
slower in a damp atmosphere than in a dry one. 

In case of accident to the sand-glass, time the log-line by a 
watch. 

When a vessel is going at a high rate of speed it is usual to use 



32 THE NAVIGATORS pocket-book 

a 14 seconds glass and then double the indicated number of knots ; 
this saves the paying out of a long length of line and the at- 
tendant effort of hauling it in. 

The first knot on the log line is measured from the white rag, 
which terminates the ten fathoms allowed to drift the chip far 
enough astern to be out of the eddies of the wake. When this 
white rag passes over the taffrail the sand-glass is turned. 

CHRONOMETER. — A marine time-piece constructed with 
the idea of great accuracy, and set to the time of some first me- 
ridian. The Americans and English use the time of the me- 
ridian of Greenwich ; the French that of Paris, etc. 

Care of Chronometers. — Chronometers should be wound at 
the same hour each day, the key being turned gently so that no 
shock may be imparted when the key butts. They should be 
stowed as near the centre of motion as possible, and the tempera- 
ture near them kept as uniform as possible. When transported 
by hand they should be clamped securely by the clamp-screw, 
to prevent them from swinging about in their gimbals. In wind- 
ing a chronometer the instrument is to be inverted with the left 
hand and the key turned with the right. At all times, except 
when being transported by hand, the chronometer must be left 
to swing freely in its gimbals, like a compass. Never stow a 
chronometer close against an iron bulkhead, or near an iron 
stanchion, or, beyond all, near spare compasses or artificial 
magnets, otherwise magnetism will be induced into the steel 
balance and ruin the going of the chronometer. Avoid placing 
a chronometer in the after-end of a screw steamer on account of 
the vibration . When a chronometer is being transported by hand 
be careful not to knock it against anything or to give it a sud- 
den twist. (See Rate.) 



THE NAVIGATOR'S POCKET-BOOK 33 

CHRONOMETER COMPARISON. — To determine the 
error of a chronometer by observatory clocks or by comparing 
the longitude of the ship found by observation with the known 
longitude of a visible point of land. 

CHRONOMETER RATE.— (See Rate.) 

CHRONOMETER-TIME SIGHT.— (See Longitude.) 

CIRCUM-MERIDIAN ALTITUDE. — An altitude of a 
heavenly body observed a short time before or after its meridian 
passage. This is also known as an ex-meridian altitude. (See 
Latitude.) 

CIRCUMNAVIGATE.— To sail completely around. To 
sail around the world is to circumnavigate it. 

CIRCUMNAVIGATOR'S DAY. — In circumnavigating 
the globe by sailing west the ship and the sun move in the same 
direction, but by sailing east the ship and the sun move in oppo- 
site directions. In the former case the sun overtakes the ship, 
and in the latter case the sun advances to meet the ship. There- 
fore in sailing west the ship's day is lengthened and in sailing 
east it is shortened at the rate of one hour for every 15° of 
longitude made. 

Should a vessel start from Greenwich and sail east until the 
meridian of 180° was reached, arriving at that point at 2 o'clock 
in the morning of Sunday, the 20th day of the month (according 
to the ship's date and time), it would only be 2 o'clock in 
the afternoon at Greenwich on Saturday, the 19th. Thus the 
ship's time w r ould be twelve hours ahead of the time at Green- 
wich. Now if the ship, without changing her date, continued 
sailing to the eastward until Greenwich was reached, another 
twelve hours w r ould be gained, and the ship's time would be 
twenty-four hours, or one day, ahead of the Greenwich time. 
3 



34 THE NAVIGATOR'S POCKET-BOOK 

On the other band, should a vessel start from Greenwich and 
sail west until the meridian of 180° was reached, arriving at that 
point at 2 o'clock in the morning of Sunday, the 20th day of 
the month (according to the ship's date and time), it would be 
2 o'clock in the afternoon of the same day (Sunday, 20th) at 
Greenwich, so that the ship's time would be twelve hours behind 
the Greenwich time. If the ship, without changing her date, 
continued to sail to the westward until Greenwich was reached, 
another twelve hours would be lost, and the ship's time would 
be twenty-four hours, or one day, behind the Greenwich time. 

Rule. — When crossing the meridian of 180°, if the ship is 
sailing eastward, the navigator must reckon the given day over 
again, so that there will be two Sundays, or Mondays, or Tues- 
days, etc., in the log-book for that particular week, according to 
the day that he crosses. By doing this the ship's date will be 
found to correspond with the Greenwich date when the vessel 
reaches that port. 

But w T hen crossing the meridian of 180°, if the ship is sailing 
westward, the navigator must skip a day, so that there will be a 
Sunday, or a Monday, or a Tuesday, etc., omitted in the log- 
book for that particular week, according to the day that he 
crosses. This insures the ship's date agreeing with the Green- 
wich date when the vessel reaches the latter port. 

Warning. — The great point for the navigator to bear in mind 
is that he is not to interfere with the Greenwich date shown by 
the chronometer, but that he is religiousty to keep the run of 
and hold on to same, and select the sun's declination, equation, 
etc., from the nautical almanac for the Greenicich date, and cor- 
rect the hourly difference of declination, etc., according to the 
regular rule given under the head of Declination. 

Examples. — A ship leaves Greenwich and sails east, reaching 



THE NAVIGATOR'S POCKET-BOOK 35 

the meridian of 180° on Sunday, the 20th (according to the 
ship's date). Instead of calling the next day Monday, the 21st, 
it must be considered again as Sunday, the 20th, so that two Sun- 
days and two 20th days for that month will appear in succession 
in the log-book. 

A ship leaves Greenwich and sails icesi, reaching the meridian 
of 180° on Sunday, the 20th (according to the ship's date). In- 
stead of calling the next day Monday, the 21st, it must be con- 
sidered as Tuesday, the 22d, so that there will not appear either 
a Monday or a 21st day for that month in the log book. 

CIVIL TIME. — The civil day consists of twenty-four hours ; 
it commences at midnight, and the first twelve hours are called 
a.m., and the latter twelve hours are called p.m. (See a.m. p.m.) 

CLAMP-SCREW.— (See Sextant.) 

CLOUDS.— (See Weather.) 

COLLIMATION.— The line of sight in the direction of any 
object. (See Axis of Collimation.) 

COMBINED ALTITUDE PROBLEM.— (See Sumner's 
Method.) 

COMPASS. — The mariner's compass consists of a magnetized 
steel bar secured parallel to the north and south line of a circu- 
lar card, which latter is balanced on a pi^ot so as to turn freely 
in the horizontal plane and to indicate the magnetic meridian. 
The surface of the card is divided into thirty-two courses with 
their intermediate quarters, and in addition to this all steam- 
ships have the circumference of the compass card graduated into 
degrees. 

Boxing the Compass. — What is known as boxing the com- 
pass is calling the thirty-two courses in order from north by the 



3G THE NAVIGATORS POCKET-BOOK 

way of east, as shown on the diagram in front of this book. 
To box the compass backward is to call the courses from north 
by the way of west, or contrary to the order in which the hands 
of a watch revolve. 

Points and Degrees. — By consulting the diagram it will be 
seen that compass courses are given a value both in points and 
degrees, the same commencing at the two poles of the circle 
(north and south) and ending at the equator line of the compass 
(east and west). Thus the north and south points are zero and 
the east and west points have a numerical value of 8 and an 
angular value of 90°. 

Variation of the Compass. — The compass needle when un- 
influenced by deviation points to the magnetic poles of the earth, 
and as these do not coincide with the true or geographical poles, 
the magnetic meridians form an angle with the true meridians, 
and this is called the variation of the compass, which varies in 
extent in different parts of the world. The magnetic north pole 
is situated on the parallel of 70° north and the meridian of 97° 
west. The magnetic south pole is situated on the parallel of 70° 
south and the meridian of 145° east. 

Over the North Atlantic, the greater part of the South At- 
lantic, and the Indian Ocean, the variation is westerly, and over 
a part of the South Atlantic and in the -Pacific the variation is 
easterly. There are places on the surface of the globe where 
variation does not exist, or in other words, where the compass 
points true north, and these places are said to be situated on the 
line of no variation. One of these lines runs through Eastern 
Europe, Asia, and Australia ; the other through North Ameri- 
ca, the eastern part of South America, and the southwestern 
part of the South Atlantic Ocean. 

The magnetic equator is not the same as the earth's equator, 



THE NAVIGATOR'S POCKET-BOOK 37 

but an irregular line running round the globe, near the earth's 
equator, which it crosses in two places, one near the west coast 
of Africa, the other about the middle of the Pacific Ocean. 

The variation of the compass is not constant, but undergoes 
an annual change, and the amount of this yearly increase or de- 
crease will be found plainly marked on charts. 

Deviation of the Compass. — What is known as the devia- 
tion of the compass is the deflection of the needle from the 
magnetic meridian, caused in iron sailing ships by the attraction 
of the hull and iron lowermasts, and in an iron steamship by 
the attraction of the hull, machinery, smokestack and masts. 
In addition to this it must be understood that deviation is often 
caused by certain elements of magnetism in the cargo. The 
manner of ascertaining the existence and extent of compass de- 
viation will be found explained under the heads of Amplitude 
and Azimuth. When shaping a course, or when taking com- 
pass-bearings, the deviation existing for the ship's head must be 
considered, as explained under the head of Chart Sailing. De- 
viation is named east or west according as the north point of 
the compass is drawn to the eastward or westward of the mag- 
netic meridian. 

Deviation Card. — This is a tabulated account of the devia- 
tion of the compass for each one of the thirty-two courses, and 
directs the navigator as to the course to be steered by compass 
in order to make the required correct magnetic course. Devia- 
tion always refers to the ship's head. In other words, where 
deviation is given it means for a certain course. If the card 
tells us that for an east course the compass has 10° of westerly 
deviation, it signifies that when the ship heads east the north end 
of the compass needle will be drawn 10° to the westward of the 
correct magnetic north, and any bearing taken when the ship is 



38 the navigator's pocket-book 

on such course must be corrected for 10° of westerly deviation, 
and not for the deviation given for the point represented by the 
bearing. 

A deviation card refers to one particular compass, and to no 
other, consequently a course set or a bearing taken by a certain 
compass must have the deviation of that compass applied to it 
according to its own deviation card. 

Residual Errors. — When a compass is affected by deviation 
it is sought to adjust it by placing artificial magnets in its 
vicinity, so as to draw the compass needle to the correct mag- 
netic meridian, and the remaining deviations for the various 
courses are classed as residual errors. 

Loeal Attraction of the Compass. — Elements of magnetism 
outside (away) from the vessel which influence the pointing of 
the compass. In sailing very close along some coasts where 
there are large deposits of iron ore or volcanic disturbances the 
compass has been found to be slightly and temporarily drawn 
away from the correct magnetic north. It will be understood 
that, as its name implies, this disturbing quantity is purely 
local. A vessel's compass is often affected when lying alongside 
of a dock or other vessel, owing to the near presence of iron 
used in construction of same. (See Compensated, Demagnet- 
ized, Dry, Elevated, Liquid, Masthead, Oil, Pole, Spirit, Stand- 
ard, Steering, and Tripod Compasses.) 

COMPASS ADJUSTING.— Correcting a compass for devia- 
tion by placing artificial magnets in its immediate vicinity, so as 
to draw the north end of the compass needle to the correct mag- 
netic north. As a rule compass adjusting-is performed by pro- 
fessional adjusters, it being a profession in itself, "although there 
are shipmasters who have made a study of the science, and in 
consequence are able to dispense with outside talent. In the 



THE NAVIGATOR'S POCKET-BOOK 39 

case of tlie patent-adjusting-binnacle compass, where the mag- 
nets are contained in racks within the binnacle stand, full direc- 
tions for adjusting the compass are furnished with the instru- 
ment. 

COMPASS-BEARING.— The direction of an object accord- 
ing to one of the divisions of the compass card. 

COMPASS CARD. — The circle to which is secured the mag- 
netized bar of steel and on which circle the thirty-two compass 
courses are shown. 

COMPASS CORRECTIONS. — Allowances for variation 
and deviation. 

COMPASS COURSE.— The track made by a vessel accord- 
ing to one of the divisions of the compass card. 

COMPASS NEEDLE.— The name often applied to the 
magnetized steel bar secured to the compass card. 

COMPASS POINT.— One of the divisions of the compass 
card. 

COMPASS ROSE. — The diagram compass on a chart is 
referred to in some works on navigation as a compass rose. 

COMPENSATED COMPASS.— An adjusted compass; a 
compass that has been freed, to a greater or less extent, of its 
deviation by the employment of artificial magnets, the same 
being placed in close proximity to the compass, so as to draw 
the needle to the correct magnetic meridian. 

COMPENSATING MAGNETS.— Artificial magnets used 
in compass adjusting. (See Magnet.) 

COMPLEMENT.— The full number or quantity; what an 
altitude lacks of 90° . The zenith distance is the complement 
of the altitude. 



40 THE NAVIGATOR'S POCKET-BOOK 

CO-LATITUDE.— The complement of the latitude, or what 
it lacks of 90°; as, for instance, 50° is the co-latitude of 40°. 

COMPOSITE SAILING.— This is a combination of great- 
circle and parallel sailing, and is adopted when the great-circle 
track, by passing in the neighborhood of ice, land, or other dan- 
ger, becomes impracticable. In other words, it is a modification 
of the great-circle track. (See Great- Circle Sailing.) 

CONSTELLATION.— A group of stars to which is given 
the name of some classical hero, beast, bird, fish, figure, etc. 
The Pole Star is in the constellation of Ursa Minor (The Little 
Bear), and the Dipper is in the constellation of Ursa Major (The 
Great Bear), etc. (See Fixed Stars ; Planets.) 

CORRECTED ALTITUDE.— The observed altitude of a 
heavenly body, with allowances made for dip, refraction, etc. 
(See Eighty-Nine-Forty-Eight.) 

Sun. — If the altitude of the sun's lower limb is measured, the 
semidiameter (Nautical Almanac) must be added, but if the 
upper limb is observed, the semidiameter must be subtracted, 
in order to obtain the altitude of the sun's centre from the hori- 
zon. For practical purposes the semidiameter of the sun may 
be called 16'. 

Parallax (Table 16) is always added, because the body appears 
lower when viewed from the surface of the earth than it would 
if observed from the earth's centre — except when the body is in 
the observer's zenith when it has no parallax. 

Dip (Table 14) is always subtracted, as the elevation of the 
observer's eye above the sea-level causes the navigator to meas- 
ure too great an altitude. 

Refraction (Table 20) is always subtracted, owing to the body 



THE NAVIGATOR'S POCKET-BOOK 41 

being seen above its true place, except when it is in the zenith 
of the observer, when it has no refraction. 

Moon. — The semidiameter (Nautical Almanac) of the moon 
and the dip (Table 14) are applied in exactly the same manner as 
explained for the sun ; but parallax in the case of the moon is 
large as compared with refraction, and it is so arranged that the 
moon's parallax (Table 23) is given minus the refraction, so that 
the figures selected from this table must always be added to the 
altitude. For practical purposes the semidiameter of the moon 
may be called 16', the same as the sun. 

Planets — The altitudes of these bodies are corrected for 
dip (Table 14) and refraction (Table 20) as usual, but the correc- 
tion for parallax involves a new process. With the planet's hori- 
zontal parallax (Nautical Almanac) and the observed altitude, 
find the planet's parallax (Table 17) by applying the first two 
quantities in their respective columns. The semidiameters of 
the planets are given in the almanac, and if used must be 
applied as usual, but it is to be explained that for practical pur- 
poses the altitude of a planet is never corrected for semidiam- 
eter and parallax. 

Stars.— The altitudes of the stars are corrected for dip (Table 
14) and refraction (Table 20) as usual ; they have no apparent 
diameter or parallax. 

Recapitulation. — Note the following: 

Semidiameter is always added for the lower limb and sub- 
tracted for the upper limb. 

Parallax is always added. 

Dip is always subtracted. 

Refraction is always subtracted. 

It is to be remembered that the sextant's index error (if it has any) 
is always to be figured as an altitude correction. (See Sextant.) 



42 the navigator's pocket-book 

CORRECTED COURSE.— As a preliminary to working 
out a ship's position by dead-reckoning, the compass courses 
that have been sailed are converted into true or geographical 
courses by correcting them for leeway, deviation, and varia- 
tion. 

Leeway. — The amount is determined as explained under the 
head of Leeway, and this quantity is allowed to leeward of the 
compass course. For example, if the course sailed was east 
and the vessel was on the starboard tack making one point of 
leeway, the same must be allowed toward the north, making the 
so far corrected course east- by-north. 

Deviation. — Westerly deviation must be allowed away from 
the compass course in a direction contrary to the way that the 
hands of a watch revolve. For instance, if the course after be- 
ing corrected for leeway is east-by-north, and there is one point 
of westerly deviation to be considered, the same must be allowed 
toward the north, making the correct magnetic course east- 
northeast. On the other hand, easterly deviation will be al- 
lowed away from the compass course in a direction the same 
as the hands of a watch revolve. To illustrate : if the course is 
east-by-north, and there is one point of easterly deviation to be 
considered, the same must be allowed toward the east, making, 
in this case, the course east. 

Variation.— This is allowed in exactly the same way as 
explained for deviation, as will be seen following : we will say 
that the compass course after being corrected for leeway and 
deviation is east-north-east, and that there is one point of west- 
erly variation to be considered. In this case the true or geo- 
graphical track that the ship has made is northeast-by-east. 

Again, suppose that the compass course after being corrected 
for leeway and deviation is east, and that there is one point of 



THE NAVIGATOR'S POCKET-BOOK 43 

easterly variation to be considered. In this case the true or 
geographical track that the ship has made is east- by -south. 

Remarks. — When the variation and deviation are of the same 
name (both east or both west) they may be added together and 
applied. 

If the variation and deviation are of contrary names they may 
be subtracted one from the other and the balance applied in the 
name of the greater of the two quantities. 

It is to be explained that leeway made on the starboard tack 
is applied in the same direction as westerly variation and devia- 
tion, and that leeway made on the port tack is applied in the 
same direction as easterly variation and deviation ; consequently 
there are times when the three quantities of leeway, variation, 
and deviation may be added together and applied as a whole to 
a compass course. 

CORRECTED LOCAL TIME.— To ascertain the correct 
local time at the ship, proceed as follows : to the sun's time 
shown by the ship's clock (set when the sun crossed the ship's 
meridian) add four minutes for every degree of longitude sailed 
east since the clock was last set, but subtract four minutes for 
every degree sailed west ; the answer will be the local apparent 
time at ship. 

COURSE AND DISTANCE.— (See Chart Sailing ; Great- 
Circle Sailing ; Mercator's Sailing ; Middle Latitude Sailing.) 

COURSE MADE GOOD.— The bearing of the vessel from 
the latitude and longitude last determined, irrespective of the 
traverse sailed. (See Dead-Reckoning.) 

COURSE PROTRACTOR.— This consists of a half circle of 
thin horn or isinglass, having its circular edge graduated into 
degrees, and a long thread leading from the centre of the instru- 



44 the navigator's pocket-book 

ment. To ascertain the course by tliis little contrivance place 
its zero line on any convenient meridian on the chart, then slide 
it up or down on this true north and south line until the thread 
lies in a straight line over the position of the ship and the place 
sought. The course between the two points will be indicated in 
degrees on the circle by the direction of the thread. 

Remarks. — The course protractor always gives the true or 
geographical course, to which must be allowed the variation of 
the compass for the locality of the ship in order to convert it into 
a magnetic course. If deviation exists for the compass course 
found, then this quantity must also be applied. (See Chart 
Sailing.) 

CROSS-BEARINGS.— (See Chart Sailing.) 

CULMINATE. — When a heavenly body crosses the meridian 
of the observer it is said to culminate. Upper culmination is 
when a heavenly body crosses the meridian above the pole, 
and lower culmination is when it crosses the meridian below 
the pole. What is known as a moon-culminating star is one that 
comes to the meridian at the same time with the moon. 

CURRENT. — A progressive motion of the water of the sea at 
a certain place ; an ocean river. The flow of a current is named 
according to the direction in which it sets, hence a northeast 
current comes out of the southwest and flows toward the 
northeast. (See Patent Log.) 

CURRENT LOG.— Same as ground log, which see. 

CURRENT SAILING. — When a vessel experiences a cur- 
rent, the effect is to set her in the direction of its flow. This 
must be considered as a regular and separate course, and the 
hourly velocity of the current is to be taken as the rate of speed 
made on such course, as shown following : 



THE NAVIGATOR'S POCKET-BOOK 45 

Example. — A ship while sailing southeast enters the Gulf 
Stream at a point where it is flowing northeast at the rate of two 
knots per hour, and remains in the stream ten hours. This data 
is recorded in the log-book, and when working out the dead- 
reckoning this course of northeast must be entered on the trav- 
erse table, and the distance of twenty miles considered as the 
number of knots sailed on that course. 

Remarks. — The chart will give the flow of the current either 
as true or magnetic. If the former, no correction is to be ap- 
plied to it after entering it on the traverse table ; but if the latter, 
then the variation must be applied in order to convert it into a 
true course. The deviation of the compass never enters into 
this consideration, because the direction is given by the chart. 
(See Patent Log.) 

CUT. — When referring to the graduation of the sextant arc, 
it is said to be cut to ten minutes (10'), and the vernier is said to 
be cut to ten seconds (10"). 

CYCLONE— (See Law of Storms.) 

DANGER ANGLE— (See Chart Sailing.) 

DANGER-ANGLE TABLES.— Tables that give by mere 
inspection the distance of a vessel from a certain object. In this 
consideration the known height of the lighthouse and the verti- 
cal angle of the same measured to the surface of the water are all 
that is required for the navigator to ascertain his distance from 
the object. The danger-angle tables found in the back of this 
book have been arranged by the author to the nearest 10" of arc 
(that being the lowest graduation shown on sextants) and extend 
from thirty feet to three hundred and twenty feet. The manner 
of using these tables is explained under the head of Chart Sail- 
ing. To determine the distance of a vessel from a lighthouse 



46 THE NAVIGATOR'S POCKET-BOOK 

when beyond the limit of the figures in the danger-angle tables, 
the " Distance" table in the back of this book may be employed. 

DARKS. — Having reference to those nights during which the 
moon is not seen in the heavens. 

DAY. — (See Astronomical Day ; Circumnavigator's Day ; 
Gained Day ; Lost Day ; Lunar Day ; Sea Day ; Sidereal Day ; 
Solar Day.) 

DAY'S WORK.— The calculation of the ship's latitude and 
longitude by dead-reckoning. 

DEAD-RECKONING.— The position of the ship found by 
referring the true courses to the nautical tables and selecting for 
each course the respective amounts of latitude and departure, 
then applying the aggregate value of these to the latitude and 
longitude left. The manner of converting compass courses into 
true or geographical courses is explained under the head of 
Corrected Course. 

To Find the Latitude and Longitude. — Convert the compass 
courses sailed into true or geographical courses by applying the 
leeway, deviation, and variation. With the distance made on 
each course, find separately (Table 1 or 2) the difference of lati- 
tude and departure. After selecting for all, foot the columns of 
the traverse table, and if both northing and southing have been 
made subtract one from the other ; also if both easting and west- 
ing have been made subtract one from the other. 

Apply the difference of latitude to the latitude left, adding 
the same if the ship has sailed toward the poles, but subtracting 
if the ship has sailed toward the equator ; the answer will be the 
latitude by dead-reckoning. 

Next turn to the page (Table 2) marked with the degrees of the 
middle latitude, apply the departure in the latitude column (read- 



THE NAVIGATOR'S POCKET-BOOK 47 

ing from top of page if the degrees of the middle latitude were 
found there, but from the bottom if the degrees were found 
there), and opposite to the left in the distance column will stand 
the difference of longitude. Apply this latter to the longitude 
left, adding the same if the longitude has been increased, but sub- 
tracting if the longitude has been decreased ; the answer will be 
the longitude by dead-reckoning. 

To Find the Course and Distance. — With the difference of 
latitude and departure, make them compare (Table 2) in their 
respective columns opposite each other, and in the distance 
column to the left will be seen the distance in nautical miles 
made good, and the true or geographical bearing (called course 
made good) of the vessel from her former calculated position 
will be read in degrees from the top of the page if the difference 
of latitude is greater than the departure, but from the bottom of 
the page if the departure exceeds the difference of latitude. 

Remarks. — If the vessel has been sailing in a current, or has 
been hove-to, or has taken farewell from the land, these are con- 
siderations for the traverse table. (See Current Sailing ; Depart- 
ure ; Drift.) 

Sailing-vessels steer by quarter points, but steamships steer by 
degrees, consequently in the former sailing, Table 1 is employed, 
and in the latter sailing Table 2 is made use of. 

To select the difference of latitude and departure, apply the 
distance sailed on the particular course in the column marked 
" Dist." in the tables, then read the figures in the two right- 
hand columns. If the course was found at the top of the page 
the latitude and departure must be read from the top ; but if 
the course was found at the bottom of the page the latitude and 
departure must be read from the bottom. 

DECLINATION.— The angular distance of a heavenly body 



48 the navigator's pocket-book 

north or south of the equinoctial. Declination may be expressed 
as celestial latitude. The declinations of the sun, moon, planets, 
and stars are to be corrected as explained following : 

Sun.— Select from the Nautical Almanac the sun's declination 
for Greenwich noon of the Greenwich date, and correct this for 
the hourly difference of declination by multiplying the latter 
by the number of hours that the chronometer showed before or 
past noon at Greenwich at the time the altitude was measured, 
and either add this correction to or subtract it from the declina- 
tion given for Greenwich noon, according as the declination is 
increasing or decreasing. The idea is to ascertain the distance 
of the sun north or south of the equator at the time of observa- 
tion. (See Inclination.) 

Moon. — Convert into astronomical time and date the Green- 
wich time shown by chronometer when the moon's altitude was 
observed, calling the hours numerically from one to twenty-four 
instead of referring to them as a.m. and p.m. For example, 
if, when the observation was taken, the chronometer showed 
Greenwich civil time November 5th, 8 p.m., both date and hour 
would be astronomical, and would stand as such ; but if the 
chronometer showed Greenwich civil time November 5th, 2 
a.m., then call the astronomical date November 4th and the time 
fourteen hours. (See Astronomical Time.) 

Now turn to the Nautical Almanac, and under the astronomical 
date and opposite the astronomical hour select the moon's dec- 
lination given. Opposite to this to the right will be seen the 
moon's change of declination for one minute of time. Multiply 
this minute difference by the number of minutes over the even 
astronomical hour, and if the moon's declination is increasing 
add the correction to the declination given for the hour ; but if 
the moon's declination is decreasing subtract the correction. 



THE NAVIGATOR'S POCKET-BOOK 49 

Planets. — The declination of a planet is given for Greenwich 
noon, and must be corrected in precisely the same manner as 
described for the sun— the hourly difference of the planet's dec- 
lination being multiplied by the number of hours shown from 
Greenwich noon by the chronometer at the time of observation, 
and this correction either added to or subtracted from the dec- 
lination of the planet given for Greenwich noon, according as 
the planet's declination is increasing or decreasing. 

Sta- s. — The declinations of the stars being practically a fixed 
quantity, no correction is necessary for the declinations given 
for those bodies— accepting the declinations for the given year 
as shown in the Nautical Almanac being all-sufficient. 

DEGREE.— The 380th part of the circumference of a circle. 
The value of a degree is 60'. A degree of latitude is equal to 
sixty nautical miles or knots, anywhere from the equator to the 
poles ; but a degree of longitude is equal to sixty nautical miles 
only on the equator. Leaving the equator, the distance between 
the meridians constantly contracts, so that at the poles there is 
no such thing as longitude, all the meridians meeting at those 
points. If it is desired to learn the distance between any two 
meridians on a certain parallel of latitude, simply open the 
nautical tables (Table 2) at the page marked with the parallel in 
question, then opposite the figures 60 in the distance column 
will be found (to the right) in the latitude column the number 
of miles between the meridians. 

Examples. — On the parallel of 40° the distance between the 
meridians is forty six nautical miles or knots ; consequently, if 
the ship started from the longitude of 74° and sailed forty-six 
nautical miles east on the parallel of 40°, she would reach the 
longitude of 73°. 



50 THE NAVIGATOR'S POCKET-BOOK 

On the parallel of 47° the distance between the meridians is 
40.9 (forty and nine-tenths) nautical miles. 

DEMAGNETIZED COMPASS.— A compass the needle of 
which has parted with its magnetism. 

DEPARTURE. — The amount of easting or westing made by 
a vessel from a certain point. To "take departure" is to ob- 
serve the bearing of and calculate the distance of the vessel from 
a lighthouse or other point when the harbor is cleared and the 
first course set. This is also known as "taking farewell." 

Example. — Departure is taken, Sandy Hook light bearing 
west by compass, distant six miles. This is entered as a mem- 
orandum in the column of remarks in the log-book, and when 
working up the dead-reckoning the navigator must set down in 
the traverse table, as a regular compass course and distance 
sailed by the ship, east, six miles. The latitude and longitude of 
Sandy Hook light being accepted as a point of farewell, the 
opposite point to the bearing of the light and the distance from 
it must be considered as having been sailed ; otherwise the ship 
would be six miles out in her dead-reckoning. 

This course of east must be corrected for the deviation of the 
compass for the ship's head (if deviation exists), also for the 
variation of the compass given by the chart for the locality of 
the vessel ; this will convert it into a true or geographical course. 
(See Corrected Course.) 

DEVIATION.— (See Compass ; Amplitude ; Azimuth ; Cor- 
rected Course.) 

DIP. — A heavenly body is understood to dip when it disap- 
pears below the horizon. When a heavenly body crosses the 
meridian of the observer the limb of its image, as viewed in the 



THE NAVIGATOR'S POCKET-BOOK 51 

sextant-glass, will drop below the horizon line, and under such 
conditions it -is said to dip. (See Dipping Needle.) 

DIP OF THE HORIZON.— As the observer's eye is natu- 
rally above the sea-level, the limit of view is called the visible or 
apparent horizon, and the angle between this and the sensible 
horizon is called the dip of the horizon, which is further ex- 
plained under the head of Corrected Altitude. 

DIPPER. — The seven stars forming the constellation of the 
Great Bear, and by means of which the Pole Star, in the tail of 
the Little Bear, can be readily found. 

DIPPING NEEDLE.— A magnetic needle suspended at its 
centre of gravity so as to move freely from the horizontal to the 
perpendicular. On the magnetic equator the needle assumes 
the horizontal, but at the magnetic poles it stands perpendicular 
or has a dip of 90°. 

DISTANCE TABLES.— Tabulated distances at which ob- 
jects can be seen at sea according to their respective elevations, 
combined with the height of the observer's eye above the sea- 
level. A distance table will be found in the back of this book. 
^See Danger- Angle Tables. ) 

DIURNAL.— Relating to the day. 

DIURNAL ARC. — The half circle described by a heavenly 
body from its rising to its setting. (See Nocturnal Arc.) 

DIVIDERS.— An instrument consisting of two pivoted legs, 
used by navigators for measuring distance on a chart, pricking 
off positions, etc. 

DOMESTIC NAVIGATION.— Generally refers to inland 
sailing. 



52 the navigatok's pocket-book 

DOUBLE ALTITUDE PROBLEM. — (See Sumner's 
Method.) 

DOUBLE STAR. — Two stars appearing so close together 
that they seem to touch. 

D. R. — Letters employed to express the word dead-reckoning. 

DRIFT. — When a ship is hove-to she will continually come 
up and fall off. The middle point between this coming up and 
falling off must be considered as her compass course, and the 
leeway, deviation, and variation applied to this compass course 
in order to obtain the true or geographical track of the ship. 

Example. — A ship is hove-to on the starboard tack ; her head 
comes up to east and falls off to east-northeast; leeway, four 
points ; deviation of the compass, one point westerly; variation 
of the compass, one point westerly. 

Now the middle point between east and east-northeast is east- 
by-north, and to this we apply the leeway, which gives us 
northeast-by-north. Next we apply the deviation and variation, 
and obtain for the true or geographical course of the ship north- 
b} r -east. 

DRY COMPASS. — A compass card enclosed in an air-cham- 
ber, commonly referred to as a dry-card compass. (See Liquid 
Compass.) 

DUMB COMPASS. — A circle of brass or other substance 
having engraved or printed on it the points of the compass. 

EARTH. — The third planet in order of distance from the sun ; 
equatorial diameter, 7,926 miles ; polar diameter, 7,899 miles. 
The difference between the two diameters (twenty-seven miles) 
is called the compression. Surface, one hundred and ninety- 
seven millions of square statute miles, of which fifty-one mill- 
ions is land ; mean distance from the sun, ninety-five millions 



THE NAVIGATORS POCKET-BOOK 53 

of miles ; circumference at the equator, about twenty-five thou- 
sand miles ; inclination to the plane of the ecliptic, 23£°. 
EARTH'S INDUCTION.— (See Magnetic Induction.) 
EIGHTY-NINE-FORTY-EIGHT. — In working latitude 
some navigators lump the correction for the lower limb of the 
sun as a constant plus 12' quantity, and simply add this amount 
to their observed altitude in order to obtain the central altitude 
of the body. They then subtract the latter from 90°, as usual, 
to find the zenith distance. Others adopt a still shorter method 
for obtaining the zenith distance : instead of adding 12' to their 
observed altitude they subtract the observed altitude from 89 D 
48' (which is 12' less than 90 r ), which at once gives the zenith 
distance. This twelve-minute or eighty-nine-forty-eight meth- 
od is liable to make an error of several miles in the answer to 
the problem when the height of eye correction (dip) is large, 
such as it would be on the deck and bridge of a vessel with a 
high freeboard. Altitudes should always be corrected as ex- 
plained under the head of Corrected Altitude. 

ECLIPTIC— The apparent path of the sun around the earth, 
but the earth's real path. (See Inclination.) 

ELEVATED COMPASS.— A masthead or a pole compass 
raised above the deck for the purpose of getting it beyond the 
magnetic influence of the ship's iron and machinery. 

ELEVATED POLE.— The pole which is above the horizon. 
The elevation of the pole is the altitude of the pole above the 
true horizon, and it is equal to the latitude of the place. 

EPHEMERIS. — An unabridged astronomical almanac. 

EPITOME. — An abridged treatise, such as an epitome of 
navigation. 



54 the navigator's pocket-book 

EQUAL ALTITUDES.— (See Longitude.) 

EQUATION OF TIME.— The difference between mean and 
apparent time. The equation of time selected from the Nautical 
Almanac for Greenwich noon of the given Greenwich date must 
always be corrected for the number of hours shown from Green- 
wich noon by the chronometer when the altitude of the heavenly 
body was measured. 

Rule. — Select from the Nautical Almanac the equation of time 
for the given Greenwich noon, also the hourly difference of 
equation, and multiply the latter by the number of hours shown 
from Greenwich noon by the chronometer when the observation 
w r as taken ; then either add this correction to or subtract it 
from the equation given for Greenwich noon, according as the 
equation of time is increasing or decreasing. The idea is to 
find the equation of time for the hour of observation. (See 
Mean Sun.) 

EQUATOR. — The imaginary line encircling the earth, equi- 
distant 90° from the north and south poles. 

EQUINOCTIAL The celestial equator. 

EQUINOCTIAL POINTS.— (See First Point of Aries.) 

EQUINOX. — (See Autumnal Equinox ; Vernal Equinox.) 

ERROR OF COLLIMATION.— (See Axis of Collimation.) 

EVENING STAR.— (See Morning Star.) 

EX-MERIDIAN.— (See Latitude.) 

FARE WELL.— (See Departure. ) 

FATHOM.— (Six feet.) 

FINDING THE TIME.— (See Regulating.) 



THE XAYIGATOR S POCKET-BOOK 00 

FIRST MERIDIAN,,— (See Prime Meridian ; Circumnavi- 
gator's Day.) 

FIRST POINT OF ARIES.— That point of the ecliptic 
which the sun crosses on March 21st from the south to the 
north side of the equator. The point of the ecliptic which the 
sun crosses on September 23d from the north to the south 
side of the equator is known as the First Point of Libra. These 
two points are termed the Equinoctial Points, and when the 
sun crosses them the lengths of the days and nights are equal 
throughout the world. The First Point of xAries is the Spring 
(or Vernal) Equinox, and the First Point of Libra is the Au- 
tumnal Equinox. 

FIRST POINT OF CANCER— That point of the ecliptic 
which the sun enters about June 21st, when its declination is 
23^° north. 

FIRST POINT OF CAPRICORN. — That point of the 
ecliptic which the sun enters about December 21st, when its 
declination is 23|° south. 
FIRST POINT OF LIBRA.— (See First Point of Aries.) 
FIXED STARS.— The term "fixed stars" applies to those bod- 
ies in the heavens which appear constantly in the same relative 
position. The fixed stars shine by their own light, and their ap- 
parent twinkling and their smaller appearance distinguish them 
from the planets. The planets are seen sometimes in one posi- 
tion and sometimes in another, the same planet being at one 
time the morning star and at another time the evening star. The 
fixed stars are separated into classes, the brightest being stars of 
the first magnitude, of which it is generally accepted there are 
nineteen ; the second in order of brightness are classed under 
the head of second magnitude and number about sixty ; next 



56 THE navigator's pocket-book 

the third magnitude, numbering about two hundred ; then follow 
fourth, fifth, and sixth magnitudes, beyond which they cannot 
be distinguished without the aid of a telescope, consequently 
such stars are known as telescopic stars. Variable stars are those 
which appear to intermit in the way of brightness, and inter- 
mediate stars are those which are divided between two magni- 
tudes, and may be seen expressed as 1-2, meaning that they are 
nearer 1 than 2 ; but if they are expressed as 2-1, it means that 
they are nearer 2 than 1. The term magnitude has no reference 
to the dimensions or masses of the stars, but only to their bright- 
ness. The word constellation means a group of stars, fanci- 
fully supposed to represent some figure, such as a classical hero, 
a beast, bird, fish, etc. The brightest stars were distinguished 
by the ancient astronomers by proper names, such as Rigel, Sir- 
ius, etc.; but the commonest practice is to use the small letters 
of the Greek and Roman alphabets to classify their degrees of 
brightness, a being prefixed to the brightest, & to the next 
brightest, and so on. When the Greek letters are exhausted the 
Roman are made use of, such as a, b, c, d, etc., and when these 
are also exhausted then numerals are made use of, such as 1, 2, 
3, 4, etc. 

The following nine stars (Arietis, Aldebaran, Pollux, Regulus, 
Spica, Antares, Aquilse, Fomalhaut, and Pegasi) are those prin- 
cipally used by navigators for finding the longitude, and the 
navigator should not rest satisfied until he has succeeded in so 
familiarizing himself with those parts of the heavens in which 
they are placed as to be able to readily refer to them. By fol- 
lowing the directions given he may soon impress their relative 
positions upon his memory. 

In the higher northern latitudes if the observer will look 
toward the north pole he will see (as shown following) a star 



THE NAVIGATOR'S POCKET-BOOK 



57 



a Arietis. 



Aldebaran. 



' Pollux. 



of the second magnitude, called the Pole Star. It 
is easily recognized because it Las no other star of 
equal brightness in its immediate vicinity, and be- 
cause it is always seen in the same direction — bear- 
ing north. Another distinguishing feature in rela- 
tion to it is the constellation of the Seven Stars, 
commonly known as the Dipper, the two stars in 
the dipper end of which (called the Pointers) point 
to the Pole Star. 

This star bears about west, distant 23° from the 
Seven Stars ; it is of the second magnitude, and 
may be known by means of a star of the third magni- 
tude, situated southwest from a Arietis, at the dis- 
tance of 3^°. South from this star, at a distance of 
H°, is a star of the fourth magnitude. 

About 35° east-southeast from a Arietis, and 14° 
southeast from the Seven Stars, is the bright star 
Aldebaran. Near this star to the westward are sev- 
eral stars of the third and fourth magnitudes, form- 
ing with Aldebaran the letter V. At the distance 
of 23° from this star, in a southeast direction, are 
three very bright stars, situated in a straight line, 
near to each other, being known as The Belt of 
Orion. 

At a distance of 45° from Aldebaran, in the di- 
rection of east-northeast, is the bright star Pollux. 
Northwest from Pollux, distant 5°, is the bright 
star Castor. 

East-southeast-half-east from Pollux, at a dis- 
tance of 37-|°, is the bright star Eegulus. North of 



58 THE NAVIGATOR'S POCKET-BOOK 

# # this star, at a distance of 8", is a star of the second 

magnitude, and further to the northward are five 

# stars of the third magnitude, the whole forming a 
* cluster resembling a sickle, Regulus being the ex- 

Regulus. * tremity of the handle. A line drawn from the 
Pole Star, through its pointers, will pass about 12° 
to the eastward of Regulus. 

'""Spica. East-southeast from Regulus, at a distance of 54°, 

* is the bright star Spica, with no other bright star 
near it. Southwest from this star, at a distance of 
about 16°, are five stars of the third and fourth 

* * magnitudes, situated as shown in adioinimr figure, 

the two northernmost of which form a straight line 
with Spica. 

East-southeast from Spica, at a distance of 46°, 
is the remarkable star Antares, being of a reddish 
color, so that it is easily distinguishable. On each 
w Antares. side of it, about 2° distant, is to be found a star of 
the fourth magnitude, these stars bearing respect- 
ively from Antares west-northwest and south- 
southeast. In the vicinity of Antares there is no 
very bright star. 

Northeast from Antares, at the distance of 60°, 

# is the bright star a Aquilse ; north-northwest of 
*a Aquilse. w ^ch, at 2° distant, is a star of the third magni- 

% tude, and south-southeast, at 3° distant, is a star 

of the fourth magnitude. These three stars ap- 
pear practically in a straight line. aAquilaa may 
be readily distinguished, as it is of a reddish nature, 
being nearly of the same color as Antares. 



Fomalhaut. 



THE NAVIGATOR'S POCKET-BOOK 59 

Southeast from aAquilve, at a distance of 60°, is 
the bright star Fomalhaut. It is in high southern 
declination, so that in northern latitudes its altitude 
is small. On the parallel of 40° north its altitude 
is about 20°. Fomalhaut bears nearly south from 
j4 the star a Pegasi, being about 45° distant. A line 
drawn from the pointers in the Dipper, through the 
Pole Star, and continued to the opposite meridian, 
will pass very near to a Pegasi and Fomalhaut. 

East-by-north from a Aquilse, at a distance of 48°, 

* and westward from aArietis, at a distance of 44°, 

* is the star a Pegasi, which may be distinguished by 

means of four stars of varying magnitudes, situated 

* as shown in the adjoining figure. The star due 

north of a Pegasi is of the second magnitude, and 

■fc a Pegasi. is distant 13°. The two close stars northwest of 

a Pegasi point to this star, and the most northern 

one of the two close stars is in line with a Pegasi 

and the most northern and western star in the 

group. 

Remarks. — To reconcile compass directions with the fore- 
going star diagrams, the navigator must hold the page upside 
down over his head, directing the top of the page toward the 
north. 

FOCAL DISTANCE. — The distance between the object-glass 
and the image. Focal length means the same as focal distance. 

FOUR-POINT BEARING.— (See Chart Sailing.) 

FURLONG. — An eighth of a mile ; == forty rods ; — two 
hundred and twenty yards ; — six hundred and sixty feet. 



60 THE NAVIGATORS POCKET-BOOK 

GAINED DAY.— (See Circumnavigator's Day.) 

GEOGRAPHICAL MILE.— A nautical or sea mile of 
6,082.66 feet ; the mean length of a minute of latitude ; a knot. 

GEOGRAPHICAL POLES.— The extremities of the earth's 
axis ; the two points of 90° north and south. 

GRADUATED. — Divided ; a scale, as, for instance, the grad- 
uated arc of a quadrant, octant, and sextant, or a graduated 
vernier. 

GRADUATED RULES.— Parallel rules having one of the 
bevelled edges divided into degrees and the other edge divided 
into quarter points of the compass. They are used for shaping 
a course and are independent of the diagram compasses on the 
chart. 

Rule. — Lay the rules on the chart on the course to be deter- 
mined so that the centre mark of the rules rests on a meridian 
line, and read the true course on the divided edge where it is cut 
by the meridian line. This true course must always have the 
variation of the compass for the ship's locality applied to it in 
order to convert it into a correct magnetic course ; and provided 
deviation of the compass exists, this quantity must also be taken 
into consideration. (See Chart Sailing.) 

GREAT-CIRCLE CHART.— (See Chart.) 

GREAT-CIRCLE SAILING.— A straight course between 
two places is the arc of a great circle. A great-circle track 
drawn on a Mercator's chart represents a curve, except on the 
meridians and on the equator, which are great-circle tracks of 
themselves. According to a great-circle track plotted on a 
Mercator's chart a ship in following it would constantly change 
the direction of her head, but in reality she would sail in a 



THE NAVIGATOR'S POCKET-BOOK 61 

straight line. This is to be explained by stating that a Merca- 
tor's chart gives a distorted view of the earth's surface. 

When a vessel, as in the case of a steamship, is navigated on 
a straight-line course on a Mercator's chart her head is never 
pointed in the exact direction of the port to which she is bound 
until that port heaves into sight ; but when following a great- 
circle track her head is from first to last pointed direct for her 
destined port. In other words, when a vessel is navigated on a 
straight line course on a Mercator's chart, her head at starting 
points toward the equatorial side of the port bound to, and 
gradually, as the voyage progresses, her head turns in the right 
direction, or toward the point of her destination ; whereas the 
great-circle track leads direct from one port to the other. 

As well as shortening the distance between two places, the 
great-circle track is of the highest importance for sailing ships, 
as it often happens that a more or less head wind according to a 
Mercator's course is made a fair wind on a great-circle course. 
The real direction of the port bound to can only be ascertained by 
consulting the great circle, and this determines whether the exist- 
ing wind is fair or ahead for the great-circle course. 

To illustrate the foregoing theory the author shows the follow- 
ing example, given by Captain S. T. S. Lecky, in his masterly 
digest of navigation entitled "Wrinkles." It proves the possi- 
bilities of the great-circle track for sailing vessels : 

Example. — "Take, for instance, the case of a vessel bound 
from Quebec to Greenock or Liverpool. The true course and 
distance by Mercator's chart from Belleisle Light -house to Inish- 
trahul Light-house is N. 83° E., 1,722 miles ; but the distance on 
the great circle is 1,690 miles, or thirty-two miles less; whilst 
the course at starting is N. 63|° E. , or 19^° more to the north- 
ward. Now if a sailing ship on clearing the Strait has the wind 



62 the navigator's pocket-book 

at east-half -north, it would at first seem immaterial on looking 
at Mercator's chart which tack she was put upon ; but if placed 
on the starboard tack she would lie up within 3^ points of the 
true direction of her port, whilst if placed on the other tack, 
instead of approaching her port she would be actually going 
away from it." 

To Draw the Great-Circle Track.— Professor Airy's exceed- 
ingly simple and valuable table for sweeping an arc of a great 
circle on a Mercator's chart on one side of the equator is given 
following, and is heartily indorsed by the author of this volume. 

Join the place of the ship and the place of destination by a 
straight line and find the middle point. 

Draw from this middle point a perpendicular line toward the 
equator and continue the line beyond the equator if found neces- 
sary in order to sweep the arc. 

With the middle latitude between the two places enter the 
following table and take out the " corresponding parallel." 

The resting-point for the sharp leg of the pencil-point dividers 
will be the intersection of the corresponding parallel with the 
perpendicular line. Place the sharp point of the dividers in 
this intersection, then with the pencil leg of the instrument 
sweep an arc that will pass through the place of the ship and 
the place of destination, and this curved line will be the great- 
circle track required. 

Changing the Course. — Except on the meridians and on the 
equator a ship must frequently change her course in order to 
keep to the great circle. Several points on the arc of the great 
circle are fixed upon, and these are made Successively by the 
ship, the course being changed with each point arrived at. 
These courses will be shaped as usual by the parallel rules and 
the diagram compasses on the chart, so that in reality a series of 



THE NAVIGATOR'S POCKET-BOOK 



63 





Corresponding Parallel. 




Corresponding Parallel. 


Middle 
Latitude. 




Middle 
Latitude. 




Opposite Name to Lat- 


Same Name as Lati- 




itude of Places. 




tude of Placss. 


20° 


81° 13' 


* 


# 


22° 


78° 16' 


#• 


* 


24° 


74 c 59' 


* 


* 


26° 


71° 26' 


* 


* 


28° 


67° 38' 


58° 


4° 00' 


30° 


63° 37' 


60° 


9° 15' 


32° 


59° 25' 


62° 


14° 32' 


34° 


55° 05' 


64° 


19° 50' 


36° 


50° 36' 


65° 


25° 09' 


38° 


46° 00' 


68° 


30° 30' 


40° 


41° 18' 


70° 


35° 52' 


42° 


36° 31' 


72° 


41° 14' 


44° 


31° 38' 


74° 


46° 37' 


46° 


26° 42' 


76' 


52° 01' 


48° 


21° 42' 


78° 


57° 25' 


50° 


16° 39' 


80° 


62° 51' 


52° 


11° 33' 


* 


* 


54° 


6° 24' 


* 


* 


56° 


1° 13' 


* 


* 



rhumb lines are employed by the navigator to enable him to 
keep his ship approximately on the great- circle. 

The sum of the distances sailed on these short courses will 
not differ much from the distance found for the great circle, 
provided the points are not too widely spaced. A very prac- 
tical method employed is to rind the change of course in points 
of the compass from the starting-place to the middle point on 
the arc of the great circle, then to turn this number of points 



64 the navigatok's pocket-book 

into quarters, and divide the distance of half the circle by the 
number of quarter points so obtained, which will give the num- 
ber of miles to sail on each quarter point. 

Example. — Suppose that between the starting-point of the 
great circle and the middle part of same the change of course 
is two compass points, and that half of the entire length of the 
great-circle track is 1,000 miles. Now in two points there are 
eight quarters, so we divide 1,000 by 8 and get 125 for an an- 
swer ; consequently we should change the course a quarter of a 
point for each 125 miles sailed. 

The navigator should bear in mind that the deviation of the 
compass must be considered in shaping the various courses on 
the great-circle track. 

Measuring the Distance. — Turn the largest course on the 
great circle (which will be one of the ends of the arc) into de- 
grees, and proceed as follows : Select the logarithms, cosecant 
of the largest course angle, cosine of the smallest latitude, and 
the sine of the difference of longitude between the two places ; 
add these three logs together, reject ten in the index, and the re- 
sult will be the sine of the distance — the degrees of which will 
be multiplied by 60 to reduce them to miles, and the minutes of 
the angle added in, and the result will be the distance on the 
great circle. 

When an angle exceeds 90°, its supplement (what it lacks of 
180°) may be used, but in this case the sine of the distance should 
be subtracted from 180°, and the answer multiplied by 60 to 
obtain the distance. 

Examples. — In the first consideration, with a course of 80° 30', 
a latitude of 40° 30', and a difference of longitude of 60° 23', 
we would obtain a distance of 2,525 miles. 

In the second consideration, with a course of 55° 57', a lati- 



THE NAVIGATOR'S POCKET-BOOK 65 

tude of 6° 48', and a difference of longitude of 140° 11', we 
would obtain a distance of 7,793 miles. 

Remarks. — By mere inspection it is possible to at once deter- 
mine if a great-circle route is practicable — that land, ice, etc., 
will not interfere. 

Great-circle sailing is valuable only in latitudes beyond the 
tropics, as within them (23° N. to 23° S.) the difference between 
the great circle and Mercator's tracks is too small to be consid- 
ered — within a few degrees of the equator all straight lines 
drawn on a Mercator's chart practically represent great-circle 
tracks. 

What is known as Mixed or Composite tracks are modifica- 
tions of the great-circle track, adopted by reason of obstacles in 
the way of the latter, such as land, etc. 

When driven a considerable distance from the great-circle 
track, the navigator should not attempt to regain it, but should 
trace a new great circle from the place of the ship. 

GREENWICH DATE.— The day of the month at Green- 
wich. If at any time there should be uncertainty concerning 
the Greenwich date it may be determined as follows : 

Express the ship's time astronomically (see Astronomical 
Time), then turn the ship's longitude into time (see Table 7, or 
Arithmetic of Navigation), and proceed according to one of the 
two rules given below : 

West Longitude. — Add the longitude in time to the ship's as- 
tronomical time : their sum, if less than twenty-four hours, will 
be the Greenwich time of the same date as at ship ; but if their 
sum is greater than twenty- four hours, reject twenty-four hours 
and put the Greenwich date one forward. 

East Longitude. — If the longitude in time is less than the 
ship's astronomical time, subtract the former from the latter, 
5 



66 the navigator's pocket-book 

and call the Greenwich date the same as the ship's date ; but if 
the longitude in time is greater than the ship's astronomical time, 
add twenty-four hours to the latter, then subtract, and call the 
Greenwich date one day less than the ship's date. 

GREENWICH TIME.— The Greenwich hour shown by a 
chronometer set to that meridian. If the ship's longitude is 
turned into time (see Table 7, or Arithmetic of Navigation) and 
added to the local time at the vessel (as shown by the ship's 
clock), when in west longitude, but subtracted from the local 
time at ship when in east longitude, the answer wili be the 
Greenwich time, independent of the chronometer. 

GROUND LOG. — An instrument for detecting the presence 
of a current when the ship is becalmed on soundings out of 
sight of land. An ordinary heaving lead is made fast to the 
regular chip log- line, then the lead is cast overboard and al- 
lowed to rest on the bottom. If there is a current, the drift of 
the ship from the lead will at once give its direction by the 
angle of the log-line, and the velocity of the current will be 
measured by the seconds glass, or watch, as explained under the 
heading of Chip Log. 

GUNTER'S SCALE.— A flat rule about two feet in length, 
marked on one side with the scales of equal parts, chords, tan- 
gents, sines, etc., and on the other side with the logarithms of 
these parts. It is employed for solving mechanically certain 
problems in navigation and surveying. 

HACK WATCH. — A common watch used by navigators, 
who set it to the time shown by the chronometer, so as to carry 
the Greenwich time with them on deck when about to measure 
an altitude. It is also set to the apparent time at ship when ob- 



THE NAVIGATOR'S POCKET-BOOK 67 

serving azimuth bearings of the sun for determining the devia- 
tion of the compass. 

HEAVE OF THE SEA. — When a vessel is sailing more or 
less in the trough of a heavy sea, the effect is to drive her to 
leeward, and this is expressed either as the heave of the sea or 
send of the sea. It goes without saying that a shallow vessel 
will be lifted off more than a deep vessel, and for that reason no 
rule can be given, the navigator being obliged from experience 
to estimate the quantity for his vessel. 

HEELING ERROR.— The change of compass deviation 
owing to the vessel being listed to port or starboard, and which is 
compensated by a vertical steel magnet placed exactly under the 
centre of the compass card. Heeling error will be at its maxi- 
mum when the vessel is heading north or south, as the north end 
of the needle will be drawn to the elevated (weather) side. 

HIGH LATITUDE.— Parallels far removed from the equa- 
tor, both in the northern and southern hemispheres. Opposed 
to low latitudes, which are parallels in the vicinity of the equator. 

HORIZON. — The apparent meeting of the sea and sky. (See 
Artificial Horizon ; Dip of the Horizon ; Sensible Horizon ; Vis- 
ible Horizon.) 

HORIZON GLASS.— (See Sextant.) 

HORIZONTAL DANGER ANGLE.— (See Chart Sailing.) 

HORIZONTAL PARALLAX.— When a heavenly body 
is on the horizon of the observer, its altitude to him is practi- 
cally zero, but another observer viewing the body at the same 
time from the centre of the earth would not see it on his horizon, 
but elevated above it ; and the difference between these two 
angles is called the horizontal parallax. 



68 the navigator's pocket-book 

HOUR ANGLE.— The angle of a heavenly body at the pole, 
between the observer's meridian and the circle of declination pass- 
ing through the body. This angle is measured on an arc of the 
equinoctial intercepted between the meridian and the circle of 
declination, and is converted into time by giving to every fifteen 
degrees (15°) a value of one hour. 

HURRICANE.— (See Law of Storms.) 
HYDROGRAPHIC CHART.— (See Chart.) 

HYGROMETER. — A wet-bulb thermometer employed by 
navigators as an adjunct to the barometer and dry-bulb ther- 
mometer in foretelling weather. This instrument is used to 
measure the amount of moisture in the air. Two equal ther- 
mometers are selected and mounted on the same frame, the 
bulb of one being left naked, while the other is tied up in a thin 
muslin covering with a cotton wick leading from it to a small 
cup of water placed beneath it and about three inches away from 
the wet-bulb thermometer. As the evaporation of the water 
produces cold, the mercury in the wet-bulb tube will stand lower 
than its companion the dry bulb, and the depression of the wet- 
bulb thermometer measures the humidity of the atmosphere. If 
the water in the muslin which covers the wet bulb be frozen, it 
will not affect the record, but will give the same reading as 
though frost did not exist. 

In frosty w r eather, to insure against the muslin becoming dry 
through evaporation, it should be wetted and allowed some little 
time to freeze before the reading is made. 

The muslin and wick should so act as to keep the wet bulb 
always wet so that evaporation may be constantly going on ; 
and it is recommended that the little muslin bag and wick be 



THE NAVIGATOR'S POCKET-BOOK G9 

changed about once a month owing to their tendency to become 
foul with grit and smoke and dust. 
When rain, fog, or dew is promised the hygrometer will rise. 

HYPOTHENUSE.— The longest side of a right-angle tri- 
angle, or the line opposite the right angle. (See Base ; Perpen- 
dicular.) 

INCIDENCE. — In the artificial horizon the image of a k body 
is reflected from the surface of the quicksilver to the eye, and 
the measured angle is always divided by 2 in order to obtain 
the altitude. This proves at once that the angle of incidence is 
equal to the angle of reflection. The angle from the body to the 
quicksilver is the angle of incidence, and the angle from the 
quicksilver to the eye is the angle of reflection. 

INCLINATION.— The inclination of the plane of the earth's 
equator to the plane of the ecliptic is about 23° 28' ; this it is 
that accounts for the declination of the sun. If the axis of the 
earth was perpendicular to the plane of the ecliptic, the sun 
would always be on the equator, and in that case the corrected 
altitude subtracted from 90 c would always be the latitude of the 
observer as well as the zenith distance of the sun. 

INDEX. — The integer part of a logarithm. (See Sextant.) 

INDEX BAR.— (See Sextant.) 

INDEX ERROR.— (See Sextant.) 

INDEX GLASS.— (See Sextant.) 

INDUCTION.— (See Magnetic Induction.) 

INSTRUMENTAL PARALLAX.— A sextant should always 
be adjusted by the horizon line at sea and by a distant line (such 
as the roof of a remote building) on shore, because the horizon 
and index glasses of the sextant are not on the same horizontal 



?0 THE NAVIGATOR'S POCKET-BOOK 

plane. When the horizontal line of a near object is used the 
sextant cannot be properly adjusted ; but when the horizontal 
line of a distant object is employed, the instrumental error is 
practically eliminated. 

INTERCALARY DAY.— A day that is inserted in the cal- 
endar out of the common order so as to preserve the correspond- 
ence between the civil and the solar year. The 29th of Febru- 
ary in a leap year is an intercalary day. 

INTERCARDINAL POINTS.— Northeast, southeast, south- 
west and northwest points of the compass. 

INTERPOLATION.— To alter by inserting something, as, 
for instance, reducing the given declination of a heavenly body 
to another time than that for which it is originally recorded. 

INTERTROPICS.— Between the tropics ; between the par- 
allels of 23i° north and 231° south. 

INVERTING TELESCOPE.— (See Sextant.) 

IRRADIATION.— The apparent enlargement of the diam- 
eters of the sun and moon. It is an optical illusion caused by 
the light of the object, and may be best appreciated in the illus- 
tration of the new moon — the bright crescent appearing to be a 
part of a larger circle than that of its shadowed disk. Irradia- 
tion increases with the brightness of the object, and diminishes 
in proportion as the illumination of the body and that of the 
field of view approach equality, vanishing when they become 
equal. This apparent augmentation is greatest in the case of 
the sun ; but even in reference to this body the amount of 
irradiation seldom exceeds 6", so that for all practical purposes 
the question need not be entertained by the navigator. 

KISS. — When the image of the moon's or sun's limb is made 



THE NAVIGATOR'S POCKET-BOOK 71 

to touch the horizon line in measuring an altitude, it is said to 
kiss the horizon. 

KNOT.— (See Mile.) 

LANDFALL. — To first make the land, to obtain the first 
view of land when coming from sea. To make what is known 
as a good landfall signifies that the navigation of the ship has 
been well performed, and that the exact point of land discovered 
is the place previously calculated on by the navigator. 

LATITUDE. — The distance of a place on the earth's surface 
north or south of the equator. Latitude is measured from the 
equator in degrees, minutes, and seconds. In a degree of lati- 
tude there are sixty geographical or nautical miles or minutes, 
each possessing a value of 6,082.66 feet. A mile of latitude 
and a minute of latitude mean the same thing. The extremities 
of the earth's axis, the north and south poles, have a value of 
90°. Latitude may be said to be the angular distance of a place 
from the equator, measured on a meridian. The following rules 
furnish the methods for finding the latitude of the ship by 
observations of the sun, moon, planets, and stars : 

Latitude by the Sun at Meridian. — Observe the altitude (see 
Altitude) and note the Greenwich hour shown by chronometer ; 
then correct the observed altitude for index error (if any), semi- 
diameter, parallax, dip, and refraction (see Corrected Altitude), 
and always subtract the answer, called the true central altitude, 
from 90° to obtain the zenith distance, which name the opposite 
to the bearing of the sun at meridian — i.e., north or south. 
Correct the sun's declination (see Declination), and if the cor- 
rected declination has the same name (north or south) as the 
zenith distance, add the two quantities ; but if they are of 
different names, subtract the less from the greater, and the an- 



72 the navigator's pocket-book 

swer will be the latitude, which will take the name of the great- 
er quantity. 

Latitude by the Sun— Ex-Meridian. — It sometimes happens 
that when the sun has climbed, almost to the meridian a passing 
cloud obscures it and that the body fails to reappear in time for 
its meridian altitude to be measured, or, on the other hand, 
there are cloudy days when the sun does not appear in the 
morning, but bursts through the clouds, temporarily or per- 
manently, some little time after meridian. Bowditch gives two 
very useful tables by which the variation of the sun's altitude 
may be found for thirteen minutes of time on each side of the 
meridian, which tables are employed according to the following 
rule : 

Rule. — Observe an altitude (see Altitude) and note the Green- 
wich hour shown by chronometer, as well as the local apparent 
time as shown by the ship's clock, which latter correct by add- 
ing to it four minutes of time for every degree of longitude sailed 
east since the clock was last set, but by subtracting four minutes 
for every degree sailed west. Now with this time from ship's 
noon enter Table 27 and select the figures given. Next with the 
latitude by dead-reckoning to the nearest degree and the sun's 
declination to the nearest degree, enter Table 26 and find the fig- 
ures by which the figures taken from Table 27 must be multiplied. 
The answer will represent the change of altitude in seconds of 
arc for the given time from noon, and this result will be divided 
by 60 to convert it into minutes of arc ; then this is always added 
to the observed altitude, whether the angle was measured before 
or after meridian, for in either case the sun was lower than it 
was at noon. Now correct this augmented altitude for semi- 
diameter, etc., and proceed precisely the same as described in 
the preceding rule for a regular meridian sight. 



THE NAVIGATOR'S POCKET-BOOK 73 

Remarks. — When the time from noon exceeds the limits of 
Table 27 (13 minutes), the augmentation of the altitude may be 
found by simply calculating the square of the given number of 
minutes, then multiplying same as usual by the figures from 
Table 26. 

Examples. — If the time from noon is 20 minutes, take out 
from Table 27 the square for 10 minutes, which is 100 ; multiply 
this by 4 and the answer will be 400— the square of 20 minutes. 
Now multiply this 400 by the quantity given in Table 26 for the 
ship's latitude and the sun's declination, and the answer will be 
the required correction to be added to the observed altitude. 

If the time from noon is 14 minutes, take out the square of 
7 minutes, w-hich is 49 ; multiply it by 4, and the answer will be 
196, the square of 14 minutes, which will be multiplied by the 
figures from Table 23. 

If the time from noon is 17 minutes, take out the square of 8 
minutes and 30 seconds, which is 72.2, and multiply it by 4, 
and the answer will be 288.8, w 7 hich will be multiplied by the 
figures from Table 26. 

Explanation. — The square of the minutes from noon may also 
be found in the following easy manner, independent of Table 
27: 

If the time from noon is 32 minutes, the required square will 
be found by multiplying 32 by its own number, hence 32 multi- 
plied by 32 equals 1,024 (32 x 32 = 1,024), which will be multi- 
plied as usual by the figures from Table 26. 

It must be remembered in using the method of ex-meridian 
that when the sun passes near the zenith (that is, when its altitude 
is high) the time from noon at which the observation is taken 
must not exceed the figures in Table 27. 

The navigator must bear in mind that the latitude found by an 



74 the navigator's pocket-book 

ex-meridian observation is the latitude of the ship at the exact 
time of the sight, and not at 12 o'clock (meridian). To carry this 
latitude forward or back to noon, it is necessary to apply to it 
the difference of latitude selected from the Table (1 or 2) for the 
course and distance made by the ship in the interval between 
the time of sight and noon. 

Latitude by the Moon at Meridian. — Observe the altitude 
(see Altitude) and note the Greenwich hour shown by chronom- 
eter. Correct the latter for its rate (see Rate), also the altitude 
for index-error (if any), semi-diameter, dip, parallax, and refrac- 
tion (see Corrected Altitude). Always subtract the answer, called 
the true central altitude, from 90° to obtain the zenith distance, 
naming the latter the opposite to the bearing of the moon at 
meridian — i.e., north or south. Correct the moon's declination 
(see Declination), and if the corrected declination has the'same 
name (north or south) as the zenith distance, add the two quan- 
tities, but if they are of different names, subtract the less from 
the greater, and the answer will be the latitude, which will take 
the name of the greater quantity. 

Latitude by a Planet at Meridian. — Observe the altitude 
(see Altitude) and note the Greenwich hour shown by chronom- 
eter. Correct the altitude for index error (if any), dip, parallax, 
and refraction (see Corrected Altitude), and always subtract the 
answer, called the true altitude, from 90° to obtain the zenith 
distance, naming the latter the opposite to the bearing of the 
planet at meridian — i.e., north or south. Correct the planet's 
declination (see Declination), and if the corrected declination 
has the same name (north and south) as the zenith distance, add 
the two quantities, but if they are of different names subtract 
the less from the greater, and the answer will be the latitude, 
which will take the name of the greater quantity. 



THE NAVIGATOR'S POCKET-BOOK 75 

Latitude by a Star at Meridian. — As the stars are passing 
the meridian at all hours of the night, it becomes a very simple 
problem to determine the latitude of the ship when the sky is 
clear and when the horizon is outlined. In the back of this 
book will be found star tables which include all the stars of the 
first magnitude both in the northern and southern hemispheres, 
and the navigation stars of the second and third magnitudes, to- 
gether with the astronomical apparent times that they cross the 
observer's meridian on the first day of each month throughout 
the year, also their rough declinations. As the times given in 
the tables for the meridian passages of the stars are calcu- 
lated astronomically, it must be remembered that from 1 to 
12 the hours agree with p.m. civil apparent time, but 13 hours 
means 1 o'clock in the morning, 14 hours means 2 a.m., 20 
hours means 8 a.m., etc. The declinations of the stars are 
practically constant, and do not require correction, but the 
small annual changes of declination are shown in the al- 
manac. 

The stars come to the meridian four minutes earlier on each 
successive day, therefore to find the time of a star's meridian 
passage for any day between the first and last of the month, 
multiply by 4 the number of days that have passed since the 
first of the month and always subtract this sum from the time 
of the meridian passage given for the first. For example, sup- 
pose that it was required to know the time of the meridian pas- 
sage of the star Sirius on the 10th of January. The differ- 
ence between 1 and 10 is 9, so we multiply the latter by 4, and 
receive 36 for an answer, and this we subtract from the time 
given for the star's meridian passage on the 1st of January (11 h. 
50 m.) and obtain 11 h. 14 m., which represents the time that 
Sirius will cross the meridian of the ship on the 10th day of 



76 the navigator's pocket-book 

January. Proceed to find the latitude in the following man- 
ner : 

Rule. — Observe the altitude (see Altitude) and correct same 
for index error (if any), dip, and refraction (see Corrected Alti- 
tude), then always subtract the answer, called the true altitude, 
from 90° to obtain the zenith distance, and name the latter the 
opposite to the bearing of the star at meridian — i.e., north or 
south. Now set the star's declination (given in the almanac) 
under the zenith distance, and if the} r are of the same name (north 
or south) add the two quantities, but if thej r are of different 
names, subtract the less from the greater, and the answer will be 
the latitude, which will take the name of the greater quantity. 

Remarks. — This star method is the shortest and simplest of 
all latitude calculations. 

Whenever it is possible the navigator should observe stars both 
north and south of him (north and soutii of his zenith), then take 
the mean of the two latitudes obtained, as this will eliminate or 
halve possible errors in thewa} :r of misjudging the horizon, etc. 

Should the navigator require the time of the meridian passage 
of a star not contained in either of the star tables in this book, 
he may calculate it readily by the following method : 

First, select the star's right ascension for the given day from 
the star page in the back of the Nautical Almanac, also the sun's 
right ascension from the almanac for the given day of the 
month. 

Second, if the star's right ascension is less than the sun's right 
ascension add twenty-four hours to the former, but if not then 
let it stand as selected. Now subtract the sun's right ascension 
from the star's right ascension, and the answer will be the astro- 
nomical apparent time of the star's meridian passage. 

Latitude by the Pole Star at Any Hour. — The following 



THE NAYIGATOK's POCKET-BOOK 77 

rule for finding the latitude at any hour of the night by the Pole 
Star when it is out of the meridian is, to a certain extent, unsat- 
isfactory, inasmuch as it cannot be depended upon to give the 
ship's position within two or three miles, although oftentimes 
with a good horizon the results are quite correct. 

Rule. — Observe an altitude (see xAltitude) at any hour when 
the star can be seen, and correct the altitude for index error (if 
any), dip, and refraction (see Corrected Altitude) ; the answer 
will be the true altitude. To the time shown by the ship's 
clock when the observation was taken add four minutes for 
every degree of longitude sailed east since the clock was last 
set, but subtract four minutes for every degree sailed west. 
Turn this corrected local apparent time into astronomical time 
by simply counting the hours from noon to noon in numerical 
order (1 to 24), instead of dividing them into a.m. and p.m. (see 
Astronomical Time). To the astronomical time at the ship al- 
ways add the sun's right ascension from the Nautical Almanac 
for the given day, and if the result exceeds twenty-four hours 
then subtract twenty-four hours and apply the remainder (which 
is called the right ascension of the meridian) in the Pole Star 
table in the back of this book, and opposite the hours and min- 
utes will be found a correction which will either be added to or 
subtracted from the true altitude, according to the given sign ; 
if + add, if — subtract. The answer will be the latitude, al- 
ways north, as the star cannot be seen south of the equator. 

Latitude by a Meridian Altitude Below the Pole. — In 
high latitudes when observing a meridian altitude of a body be- 
low the pole the altitude will grow less and less until the lowest 
part of the circle is reached, at which point the body will cross 
the meridian below the pole, after which it will commence to 
rise. 



78 the navigator's pocket-book 

To find the latitude by a body when it crosses the meridian 
below the pole, correct the altitude as usual, then obtain the 
polar distance by subtracting the body's corrected declination 
from 90°. Now add together the polar distance and the true 
altitude, and the result will be the latitude. 

Latitude by Dead-Reckoning.— (See Dead-Reckoning.) 
Latitude by the Artificial Horizon. — (See Artificial Horizon.) 
LAW OF STORMS.— When a regular wind is so obstructed 
as to produce a hurricane the wind assumes a rotary motion and 
extends over an area of from thirty to several hundreds of miles 
in diameter, revolving with greatest velocity near the vortex. 
The centre, however, of a hurricane is a space of calm in which 
frightful and confused seas are to be experienced. In the 
northern hemisphere these winds revolve contrary to the move- 
ments of the hands of a clock, and in the southern hemisphere 
they revolve in the same direction as the hands of a clock. The 
course or track followed by a hurricane is tolerably definite, as 
will be seen by the following : 

Track in the Northern Hemisphere. — The cyclone has its 
origin between the parallels of 10° and 18° north, and advances, 
or rolls forward, in a general northwesterly direction. Be- 
tween the parallels of 25° and 30 c it recurves and advances in a 
general northeaster!}^ direction . From the start and until it breaks 
up the hurricane spreads out, or increases its diameter, while 
the wind, to some extent, decreases as the area of the storm 
widens. West India hurricanes, as a rule, range between the 
parallels of 10° and 50° north and the meridians of 55° and 85° 
west, their average rate of progression being three hundred 
miles a day. 

Track in the Southern Hemisphere. — The cyclone has its 
origin in the equatorial regions (rarely within 6 C of the equator) 



THE NAVIGATOR S POCKET-BOOK 



19 



and advances, or rolls forward, in a general southwesterly direc- 
tion, and somewhere about the parallel of 25° south it recurves 
and advances in a general southeasterly direction, increasing 
in diameter from the start, and finally breaks up. 

Barometer and Weather Indications. — The barometer often 
rises suddenly just in front of a storm, owing to the air bank- 
ing up there ; consequently if the general appearance of the 
weather indicates a storm the rise of the barometer is not to 
be accepted as evidence that a storm will not be experienced, 
but rather that one is at hand. The approach of a cyclone 
may often be foretold by a greenish-tinted sky, a blood-red 
or bright yellow sunset, a heavy, unaccountable wave-swell, 
or a thick, lurid appearance of the atmosphere. A restless state 
of the barometer is another warning. After the ship has entered 
the storm disk, if a rapid fall of the barometer is experienced it 
may be accepted as evidence of a violent storm of small diam- 
eter ; but if a gradual fall of the barometer is noted, then the 
opposite conditions may be counted on. 

Distance of the Storm Centre. — The following table is given 
to show the approximate distance that has been calculated for 
the centre of the cyclone, according to the average fall of the 
barometer per hour. It is a rough calculation, but it has a 
certain value : 



Average Fall of Barometer per Hour. 



Distance in Miles from Storm Centre. 



From 0.02 in. to 0.08 in. 
" 0.06 " 0.08 " 
" 0.08 " 0.12 " 
" 0.12 " 0.15 " 



From 250 to 150. 

" 150 " 100. 

" 100 " 80. 

80 " 50. 



80 THE NAYIGATOB'S POCKET-BOOK 

Practical Considerations. — The revolving-storm problem, 
when considered practically as regards the safe navigation of 
the ship, is simple. First, locate the centre of the cyclone ; 
second, ascertain the semicircle in which the ship is ; third, 
determine the direction in which the storm is moving, and 
decide upon what course to pursue. 

Bearing of the Storm Centre. — Face the wind and note its 
bearing by compass, then, in north latitudes, count eight points 
(90°) to the right ; but in south latitudes count eight points to the 
left of the wind's eye. If the navigator in the northern hemi- 
sphere has the wind at east, the centre of the cyclone will bear 
south of him. If a navigator in the southern hemisphere has 
the wind at east, the centre of the cyclone will bear north of 
him. 

Semicircles of Storm-Disk. — The storm-disk being divided 
into two equal parts by the line or axis of the storm track, these 
two semicircles are named according to the following : Look 
in the direction toward which the storm is moving, then the 
portion that lies on the right side of this line is known as the 
right semicircle, and the portion that lies on the left side is known 
as the left semicircle. In the right semicircle the wind changes to 
the right — from north toward east, from east toward south, from 
south toward west, and from west toward north ; but in the left 
semicircle the wind changes to the left — from north toward 
west, from west toward south, from south toward east, and 
from east toward north. The first change of wind will prove 
to the navigator the semicircle he is in. 

To Avoid the Centre. — In the northern hemisphere, if the 
ship is in the right semicircle, haul by the wind on the star- 
board tack and keep going as long as possible ; but if the ship is 
in the left semicircle, bring the wind on the starboard quarter, 



THE NAVIGATOR'S POCKET-BOOK 81 

note the compass course when the ship is so headed, and keep to 
that course. In the southern hemisphere, if the ship is in the 
right semicircle, bring the wind on the port quarter, note the 
direction of the ship's head by compass, and keep to that course ; 
but if the ship is in the left semicircle, haul by the wind on the 
port tack, and keep going as long as possible. 

Tack to Heave-to On. — If obliged to heave-to, act accord- 
ing to the following simple rule : If in the right semicircle, 
heave-to on the starboard tack ; but if in the left semicircle, 
heave-to on the port tack. This rule applies to all parts of the 
world, and should be impressed upon the navigator's mem- 
ory. 

On the Storm-Track. — When the ship is on the storm track 
in front of the centre, she will not experience a change of wind, 
but will have a falling barometer and constantly increasing se- 
verity of weather ; but if in the rear of the storm-centre, she will 
have a rising barometer and a gradual moderation of the weath- 
er. In the northern hemisphere, if in front of the centre, put 
the ship before the wind, note the compass course when the 
ship is so headed, and keep to that course, and if obliged to 
heave-to do so on the port tack, but if in the rear of the centre, 
run out with the wind on the starboard quarter, or heave-to on 
the starboard tack. In the southern hemisphere, if in front 
of the centre, put the ship before the wind, note the com- 
pass course when the ship is so headed and keep to that course, 
and if obliged to heave-to do so on the starboard tack ; but if in 
the rear of the centre, run out with the wind on the port quar- 
ter, or heave-to on the port tack. 

Remarks. — When, according to the foregoing rules, a ship is 
laid-to on the port tack in the left semicircle in the northern 
hemisphere, and on the starboard tack in the right semicircle in 
6 



82 the navigator's pocket-book 

the southern hemisphere, her head will be directed toward the 
storm centre. There will be no danger in this, however, as the 
ship will not head-reach to any extent, consequently she will 
not approach the storm centre sufficient to amount to anything. 
Laid-to in this way, she will come up and bow the sea as the 
wind shifts, whereas if she was laid-to on the opposite tack she 
would be headed off with every shift of wind, and would ulti- 
mately bring the sea on the beam and quarter, and would prob- 
ably founder. 

It has been computed that West Indian cyclones, commencing 
with a very small diameter, increase the same to six hundred and 
one thousand miles before breaking up. In the Indian Ocean 
they spread out from one hundred to six hundred miles, and in 
the China Sea from eighty to four hundred miles. 

The progressive rate of the West Indian hurricane or cyclone 
is about three hundred miles a day, and the rate of the Bay of 
Bengal and China Sea c} T clones, two hundred miles a day ; but 
the rate of the Indian Ocean cyclone varies from fifty to two 
hundred miles a day. 

The cyclone season for the West Indies, Atlantic Coast of 
America, and the coasts of Mexico and Lower California is from 
July to October. The cyclone season for the Malabar Coast and 
Bay of Bengal embraces the five months of April and May, 
October, November, and December. The cyclone season for the 
China Sea extends from July to November. The cyclone sea- 
son on the coast of Japan takes in August, September, and 
October. 

LEEWAY. — The sideways drift of a vessel through the 
water owing to the pressure of the wind on her spars, sails, and 
side. Running free, a vessel jnakes no leeway, as all the wind 
and wave force exerted is on the line of her course ; but the 



THE NAVIGATOR'S POCKET-BOOK 83 

closer the ship is hauled to the wind the more she will be forced 
to leeward. When a steam vessel makes leeway owing to a heavy 
beam wind and sea, it is recorded in the log-book under the head 
of "Send of the Sea/' The manner of determining the amount 
of leeway being made by a vessel is extremely simple : It is 
only necessary to note the line of the keel by observing the 
course of the ship, then to see what angle the wake makes with 
this, and that will give at once the amount of leeway being 
made. 

Example. — A vessel, we will say, is heading east on the star- 
board tack ; the heel of her keel is west ; the wake bears by 
compass west-by-south, consequently the wake makes an angle 
of one point with the line of the keel, which amount (one point) 
is the leeway being made. Under these circumstances the ship 
is really making an east-by-north course. 

Remarks. — If a patent log is being towed, the angle made 
by the line as compared with the keel will give the amount of 
leeway. 

Some vessels have a graduated half-circle of brass tacked on 
the middle of the taff rail, and when desiring to ascertain the 
amount of leeway, either by day or night, the bight of the log- 
line is carried to this half-circle and held in the rear centre, then 
the angle made by the line with the zero point of the circle will 
give the answer either in degrees or quarter points of the com- 
pass according as the circle is graduated. 

In case the vessel is not towing a log, the hand-lead may be 
temporarily thrown overboard and allowed to trail astern, and 
the angle measured by it, as already explained. 

When the vessel is making no leeway, the wake will be left 
dead astern, but if leeway is being made, the wake will trend 
away on the weather quarter. (See Corrected Course.) 



84 the navigator's pocket-book 

LEAGUE. — A league is generally conceded to have a value 
of three nautical miles, but it varies in different countries. In 
the United States, France, Italy, and England, a league contains 
6,075 yards ; Spain, 7,416 yards ; Holland and Germany, 8,100 
yards ; Russia, 8,468 yards. 

LENS. — A piece of glass formed so as to change the direction 
of rays of light when passing through it, as the magnifying 
glasses used in telescopes. 

LIMB.— (See Upper Limb.) 

LINE. — A name for the equator. 

LINE OF COLLIMATION.— Same as axis of collimation. 

LINE OF NO VARIATION.— (See Compass.) 

LIQUID COMPASS. — A compass card enclosed and entirely 
submerged in a chamber of alcohol and water or refined petro- 
leum, to give steadiness to the card and to prevent it from flying 
about in a manner peculiar to a dry-card compass when sailing 
in rough water. 

LOCAL ATTRACTION.— (See Compass.) 

LOCAL APPARENT TIME.— Time calculated by the pas- 
sage of the sun over the observer's meridian. The length of a 
solar day varies according to the sun's movement. (See Noon.) 

LOCAL MEAN TIME. — Time calculated by the imaginary 
passage of an imaginary sun over the observer's meridian. 
This is known as the mean sun, and is adopted so as to give the 
civil day a value of exactly twenty-four hours. (See Mean Sun.) 

LOCAL TRANSIT. — The passage of a heavenly body over 
the meridian of the observer. 

LOG. — To make a memorandum of anything in the log-book 
is to " log " it. (See Chip Log ; Log-Book ; Patent Log.) 



THE NAVIGATOR'S POCKET-BOOK 85 

LOGARITHM. — A logarithm may be defined as the expo- 
nent of the power to which a given number, known as a base, 
must be raised in order to produce a certain number. By the 
employment of logarithms difficult and tedious problems in 
navigation are so simplified as to be calculated by men whose 
knowledge of arithmetic does not extend beyond the four com- 
mon rules of addition, subtraction, multiplication, and division. 
(Table 44.) 

To Select Logarithms for Degrees and Minutes. — The giv- 
en number of degrees w T ill be found at the bottom of the page 
when between 45° and 135°, otherwise at the top. The minutes 
of the angle must be found in that column marked M, which 
stands on the side of the page on which the degrees were found. 
If the degrees are found at the top of page, the sine, cosine, etc. , 
must be read from the top, but if the degrees are found at the 
bottom of page, then the sine, cosine, etc., must be read from 
the bottom. Opposite the given number of minutes will be 
found the required logarithm. 

To Select Proportions for Seconds.— The proportional parts 
will be found by the columns of differences for seconds. The 
correction of the logarithm for any number of seconds is found 
by entering the left-hand column of the table marked S' at the 
top, and finding the number of seconds in the regular minute 
column, and opposite to this in the column of differences will 
be found the corresponding correction. Thus on the page which 
contains the log. sines, tangents, etc., for 30°, the corrections for 
25" are 9 for the columns A. A. ; 12 for the columns B.B., and 3 
for the columns C.C. ; so that if it were required to find the 
sine, tangent, or secant of 30° 12' 25" we would add these cor- 
rections respectively to the logarithms corresponding to 30° 12', 
because these logarithms increase in proceeding from 30° 12' to 



86 THE NAVIGATORS POCKET-BOOK 

30° 13'. If the logarithms decreased from 30° 12' to 30° 13', we 

would subtract this correction. 

To Correct Time for Proportions of Logarithms. — In work- 
ing a chronometer sight, when selecting the time for the logarithm 
called ; ' sine of apparent time at ship," if it is impossible to match 
the logarithm in the column of sine, take the nearest logarithm to 
it, calculate the difference between the two by simple subtraction, 
and note the alphabetical sign (A.B. or C.) belonging to the col- 
umn ; then apply this difference in the little table of correction at 
the foot of page, opposite the proper letter, and find the correction 
overhead given in seconds to be added to or subtracted from the 
time corresponding to the sine accepted. This is done in order 
to obtain the full value of time for the logarithm " sine of appar- 
ent time at ship." For example : Should w r e require the p.m. 
time for the log. sine of 9.70167, we would select the nearest log. 
to this, which is 9.70159, and find by subtraction that the differ- 
ence is 8. Now the p.m. time corresponding to 9.70159 is 4 h. 01 
m. 36 sec, which we note. We now apply the 8 in the foot table 
opposite the letter A, and find a correction of three seconds over- 
head, which, in this case, we add to the time selected, making 
the same 4 h. 01 m. 39 sec. This correction is added because in 
this instance the time increases as the logarithms increase, and 
having taken out the time for an inferior log. we must add the 
correction to obtain the full measure of time for the proper log. 

To Convert Logarithms into Degrees. — Select from the 
table the degrees and minutes for the next smallest logarithm to 
the one given, then ascertain by subtraction the difference be- 
tween them, and with this difference apply it on the same page 
in the proper "Dif." column, and opposite in the M. column to 
the left will be given the number of seconds required to complete 
the degrees, minutes, and seconds. 



THE NAVIGATORS POCKET-BOOK 87 

LOG-BOOK. — The log-book is a journal of all that transpires 
of importance on board ship. Log-books in general use may be 
described as follows : 

Over the first column is marked the letter H., standing for 
the hours of the day and night, the figures below it running 
consecutively from midnight to noon (1 to 12) and then from 
noon to midnight (1 to 12), making the same divisions of the 
twenty-four hours as are used on shore. The log-book is kept 
in civil time now instead of the old method of sea time, as ex- 
plained under the head of Sea Day. 

Over the next column will be seen the letter K., standing for 
miles, or as they are nautically called, " knots." 

Next will be seen the letter F., meaning furlongs, a furlong 
standing for one-eighth of a knot. If the ship had sailed during 
the watch forty miles and a half, the half knot would be entered 
as four furlongs. Furlongs are divided by 8 to convert them 
into miles. 

Following along to the right we next find the word Courses, 
under which heading, and against the hour, will be noted the 
course of the ship by the steering compass. Every time the 
course is changed, the log must be noted, and this reading and 
the time recorded in the log-book under the proper headings. 

Next is the column of Leeway. In this column is entered the 
amount of leeway for the respective courses sailed, determined 
by the officer of the watch. 

The two following columns are for the standing of the Ther- 
mometer and Barometer. 

The last column is headed Remarks, and under this head will 
be recorded all matters of importance occurring on board, such 
as carrying away sails and spars, accidents to crew, work pro- 
gressing, also meeting with vessels, state of the weather, etc. 



88 THE NAVIGATOR'S TOCKET-BOOK 

Half way between midnight and midnight (top and bottom of 
the page) will be seen the following headings contained in red 
rulings : Course, Distance, Diff. of Lat., Departure, Lat. by 
D. R., Lat. by Obs., Variation, Diff. of Long., Long, by D.R, 
Long by Obs. We will take them up in their order in dealing 
with them : 

Course. — The bearing of the ship from her former calculated 
position is entered under this head. This is fully explained 
under the head of Dead-Reckoning. 

Distance. — On the line of bearing of the ship from the 
former position the distance is measured in a straight line, and 
set down. 

Diff. of Lat. — Here is entered the amount of latitude between 
the position last calculated and the position arrived at accord- 
ing to dead-reckoning. 

Departure. — In this space is entered the number of departure 
miles (knots) the ship is either east or west of her place last 
calculated. 

Lat. by D. R. — By applying the difference of latitude made 
to the latitude of the ship last determined, we obtain the lati- 
tude by dead-reckoning, the same being marked under this 
heading. 

Lat. by Obs. — This is calculated at noon by the sextant, and 
the result placed in this space. 

Variation. — The variations of the compass on the different 
courses are shown under this heading. 

Diff. of Long. — The number of minutes of longitude made 
(estimated by using the middle-latitude as a course in Table 2, 
and applying the whole departure) are shown under this head. 

Long, by D.R. — The longitude by dead-reckoning is found 
by applying the difference of longitude made to the longitude 



THE XAVIGATOK'S POCKET-BOOK 89 

of the ship last determined, and the same is recorded under this 
head. 

Long, by Obs. — The longitude by observation at noon (me- 
ridian) may be calculated by equal altitudes, but, as a rule, the 
morning position is carried forward to noon and the afternoon 
position is carried back to noon, in the way explained following : 

To Carry Longitude Forward.— Suppose that we should ob- 
tain a chronometer sight at 8 o'clock in the morning and 
determine our longitude at that time. Between the time of this 
sight and noon four hours elapse, and in order to find our lon- 
gitude at noon all that it is necessary to do is to correct the 
course or courses sailed since 8 a.m. ; select the departure from 
Table 2, turn it into minutes of longitude for the parallel of the 
ship, and apply this difference of longitude to the longitude of 
the ship found at 8 o'clock. Of course this will not be exactly 
the longitude by observation, but it will be so near the truth 
that for practical purposes it may be considered as the ship's 
longitude by observation at noon. 

To Carry Longitude Back — Suppose that no observation 
was secured during the morning, but that a sight was obtained 
at 4 o'clock in the afternoon. In order to carry the longitude 
back to noon so as to enter it in its column, we must find the 
difference of longitude made by the ship since noon, and apply 
it to the longitude of the ship found at 4 p.m. 

Symbols. — Letters and numbers are sometimes employed in 
log-books to represent the weather, wind, and sea. The follow- 
ing shows the various notations : 

Weather is indicated by the small italic letters : b (blue sky), 
c (detached clouds), d (drizzling rain), /(foggy), g (gloomy), h 
(hail), I (lightning), m (misty), o (overcast),^? (passing showers), 
q (squally), r (rainy), s (snow), t (thunder), u (ugly, threatening), 



90 THE NAVIGATOR'S POCKET-BOOK 

v (visibility, clearness), w (wet, dew). When a bar ( — ) is placed 
under a letter it augments its signification, and when a bar and a 
clot (—) are placed under it, it signifies heavy and continuous 
weather of the character indicated. 

Wind is denoted by the numerals, (calm), 1 (light air), 2 
(light breeze), 3 (gentle breeze), 4 (moderate breeze), 5 (fresh 
breeze), 6 (strong breeze), 7 (moderate gale), 8 (fresh gale), 9 
(strong gale), 10 (whole gale), 11 (storm), 12 (hurricane). 

Sea swell is indicated by the capital letters, S (smooth), M 
(moderate), L (long), R (rough), C (cross), H (heavy), V H (very 
heavy). 

Remarks. — Steamship log-books are ruled slightly different 
from those of sailing ships, as there is no column heading for 
leeway ; but instead there are columns for slip of wheel, etc. 
(See Current Sailing ; Departure ; Drift ; Heave of the Sea ; 
Slip of Wheel.) 

Watches. — The seven watches of the log-book are named as 
follows : 

From 8 p.m. to 12 midnight, the First Watch. 

From midnight to 4 a.m., the Mid Watch. 

From 4 a.m. to 8 a.m., the Morning Watch 

From 8 a. m. to noon, the Forenoon Watch. 

From noon to 4 p.m, the Afternoon Watch. 

From 4 p.m. to 6 p.m., the First Dog Watch. 

From 6 p.m. to 8 p.m., the Second Dog Watch. 

The reason for the watch from 8 p.m. to midnight being called 
the First Watch, is because when a ship puts to sea the first 
watch is always set at 8 p.m. The captain always stands the 
first watch out, and the mate stands the first watch coming home. 
The captain's watch is called the starboard, and the mate's the 
port watch. 



THE NAVIGATOR'S POCKET-BOOK 91 

Note. — Never ditto figures in the log-book, but where the 
same course and wind are continuous, always employ ditto 
marks, as it will keep the log-page neater, and make it easier to 
read. 

LOG-SLATE. — The deck slate on which the officer of the 
watch keeps a record of the ship's speed, course, etc., and from 
which the smooth log-book is made up. To enter anything on 
the slate is to "log" it. 

LONGITUDE. — The distance of a place on the earth's sur- 
face east or west of some given prime meridian. Longitude 
is measured in degrees, minutes, and seconds, counting as high 
as 180° east and 180° west, thus completing the circumference of 
the globe. The meridian of 180° east and the meridian of 180° 
west are represented by the same line, so that a vessel may be 
on both at the same time. Longitude may be defined as the 
angle at the pole contained between two meridians, one passing 
through the place in question and the other through some con- 
ventional point from which longitudes are reckoned. (See 
Prime Meridian.) The following rules furnish the methods for 
finding the longitude of the ship by observations of the sun, 
moon, planets, and stars. 

Longitude by Equal Altitudes of the Sun. — Observe an 
a.m. altitude (see Altitude) and at the instant of contact note the 
hour, minute, and second shown by chronometer. When the 
sun falls to the same altitude after noon, note again the chronom- 
eter. Add these two times together and divide by 2, then apply 
the rate correction, and the answer will show the mean time 
that it was at Greenwich when it was apparent noon at ship. Re- 
duce this Greenwich mean time to apparent time by applying to 
it the corrected equation of time (see Equation of Time), and if 



92 THE 

the ship is in west longitude simply turn this apparent time into 
degrees (Table 7), and the answer will be the longitude of the 
ship ; but if the vessel is in east longitude, the apparent time 
must be subtracted from 12 hours and the remainder turned 
into degrees. 

Remarks. — The time may also be converted into degrees by the 
use of the rule given under the head of Arithmetic of Naviga- 
tion. 

Observe the first altitude about half an hour before noon. 

If, after measuring the first altitude, the ship sails toward the 
sun, then the original altitude must be increased one minute of 
arc for every mile sailed between the two sights. To make this 
clear, let it be supposed that the first altitude read 20° 30' and that 
in the interval between the sights the ship sailed ten miles toward 
the sun — the instrument must be set to read 20° 40' and the sec- 
ond altitude measured by that. If, on the other hand, the ship 
sails away from the sun after measuring the first altitude, then 
the reading must be decreased one minute of arc for every mile 
sailed in the interval, and the second altitude measured accord- 
ingly. 

Longitude by One Altitude of the Sun. — Observe an altitude 
(see Altitude) and note the hour, minute, and second shown by 
chronometer at the instant of contact, and correct the latter for 
its rate ; also correct the altitude and the sun's declination (see 
Rate ; Corrected Altitude ; Declination). Next obtain the sun's 
polar distance (see Polar Distance) and add to it the true central 
altitude and the latitude by dead*reckoning, then divide the sum 
of these three quantities by 2, and from the half sum so obtained 
subtract the true central altitude, calling the answer the remain- 
der. Now select (Table 44) the logarithms, secant of the latitude, 
cosecant of the polar distance, cosine of the half sum, and sine 



THE NAVIGATOK'S POCKET-BOOK 93 

of the remainder — rejecting the index of each log. when it is 
more than 9 (see Logarithm). Add these four logs, together, 
divide by 2, and the answer will be the sine of the apparent 
time at ship when the sight was taken. With this sine, select 
(Table 44) the time standing against it, taking same from the a.m. 
column if the observation is made in the morning, but from the 
p.m. column if made in the afternoon. If the log. sine cannot be 
perfectly matched, then select the time for the nearest corre- 
sponding log. and correct the time as explained under the head of 
Logarithms. Apply the corrected equation of time (see Equa- 
tion of Time) to the apparent time at ship according to the head- 
ing of the almanac column, so as to convert it into mean time at 
ship. The difference between the mean time at ship and the 
mean time at Greenwich will be the longitude in time, which 
will be turned into degrees either by the use of Table 7 or by the 
rule given under the head of Arithmetic of Navigation. 

Remarks. — If one time is a.m., and the other time p.m., it will 
be necessary to add twelve hours to the p.m. time before subtract- 
ing—for instance, if the time at ship is 10 a.m. and the time at 
Greenwich 2 p.m., the times are four hours apart, and this is 
found by calling the Greenwich time fourteen hours and sub- 
tracting the ten hours from it. 

The best time to take sights for longitude is when the sun is 
either rising or falling rapidly, so that a considerable change of 
altitude will only affect the time to a small extent ; but do not 
use an altitude of less than 10°, owing to the uncertainty of the 
refraction. 

When the sun can be observed exactly in the prime vertical 
(when it bears true east or west) an error of a considerable num- 
ber of miles in the latitude by dead-reckoning will not produce 
a wrong result in the longitude. (See Prime Vertical.) 



94 the navigator's pocket-book 

If it is desired, several altitudes may be observed iD quick suc- 
cession, noting the corresponding times by chronometer, and the 
sum of these altitudes and times divided by the whole number of 
altitudes taken so as to obtain the mean of the altitudes corre- 
sponding to the mean of the times. This process will eliminate 
any small error that might creep into a single altitude and 
time. 

In order to understand the manner in which longitude is car- 
ried forward or back to noon from an a.m. or a p.m. sight, see 
explanation given under heading of Log-Book. 

Longitude -at Sunrise or Sunset.— Observe the sun's upper 
or lower limb to touch the horizon at rising or setting and note 
the hour, minute, and second shown by chronometer at the in- 
stant of contact, and correct the latter for its rate ; also correct 
the sun's declination and obtain the polar distance (see Rate ; 
Declination ; Polar Distance). Now add together the latitude 
by dead-reckoning and the polar distance and from their sum 
subtract 21' if the contact of the lower limb was observed, but 
subtract 53' if the contact of the upper limb was noted. Now di- 
vide the balance by 2, and to this half-sum add 21' for a lower- 
limb calculation, but add 53' for an upper-limb calculation. 
From this point select the various logarithms and proceed to 
find the longitude in precisely the same manner as directed in 
the preceding rule under the head of Longitude by One Al- 
titude of the Sun. 

Remarks. — The particular value of this working is in the 
fact that the sextant is dispensed with ; consequently, if that 
instrument meets with an accident and is rendered useless, the 
navigator is not left dependent upon his dead-reckoning for 
longitude. 

By employing a marine glass, the contact of the sun's limb 



THE NAVIGATOR S POCKET-BOOK 



95 



with the horizon may be more accurately determined than by 
the unaided eye. 

Longitude by an Altitude near Sunrise or Sunset. — At the 
time that the centre of the sun is in the true horizon (90° from 
the zenith) the lower limb has an apparent altitude of about 19' 
and the upper limb about 46'. 

A little time before sunrise or sunset, consult the following 
table and select under the figures most nearly corresponding to 
the height of eye, the altitude for the sun's lower or upper limb 
as desired, and place same on the arc of the sextant : 





Height of Eye, 13 feet. 


Height of Eye, 21 feet. 


Sun's Semi- 
diameter. 


Altitude of 

Sun's Upper 

Limb. 


Altitude of 

Sun's Lower 

Limb. 


Sun's Semi- 
diameter. 


Alt'tude of 

Sun's Upper 

Limb. 


Altitude of 

Sun's Lower 

Limb. 


/ // 


/ // 


/ // 


/ // 


/ // 


/ // 


15 45 


48 00 


18 20 


15 45 


47 00 


19 20 


16 00 


46 10 


18 10 


16 00 


47 10 


19 10 


18 15 


48 20 


18 00 


16 15 


47 20 


19 00 



With the sextant set to the required altitude, note when the 
image of the sun's proper limb is in perfect contact with the 
horizon line, and observe the hour, minute, and second shown 
by chronometer at the instant of kissing. Correct the chronom- 
eter for its rate (see Rate) and add together the logarithms tarn 
gent of the ship's latitude (by dead-reckoning) and tangent of 
the sun's corrected declination (see Declination) ; their sum, re- 
jecting ten from the index, will be the logarithm sine of an 
angle, which select from Table 44 and turn into time by Table 7, 
or by the rule under Arithmetic of Navigation. If the latitude 
and the sun's declination are of the same name (north or south) 
add the time so found to six hours at sunset, but subtract it from 
six hours at sunrise. If the latitude and declination are of con- 



96 the navigatob's pocket-book 

trary names, add the given time to six hours at sunrise, but sub- 
tract it from six hours at sunset. To this apparent time at ship 
apply the equation of time (see Equation of Time) so as to con- 
vert it into mean time at ship, after which take the difference be- 
tween it and the Greenwich mean time and turn the result into 
degrees, which will be the longitude of the ship. 

Remark. — This method should not be used beyond the par- 
allels of 40° north and south. 

Longitude by One Altitude of the Moon. — Observe an alti- 
tude (see Altitude) and note the chronometer at the instant of 
contact, to which time apply the rate correction, then turn this 
Greenwich mean time into astronomical mean time (see Astro- 
nomical Time) and next correct the moon's altitude and declina- 
tion (see Corrected Altitude ; Declination). Now obtain the 
moon's polar distance (see Polar Distance) and add to it the 
moon's corrected altitude and the latitude by dead-reckoning ; 
divide the sum of these three quantities by 2 and from this 
half-sum subtract the moon's corrected altitude. Select (Table 
44) the logarithms secant of latitude, cosecant of polar distance, 
cosine of the half-sum and sine of the remainder, rejecting the 
index of each log. when it exceeds nine. Add these four logs, 
together, divide by 2, and the answer will be the sine of a time 
which will be selected from the P. M. column (Table 44). Apply 
this time to the moon's corrected right ascension (see Right As- 
cension), subtracting it if the moon is east of the meridian, but 
adding it if the moon is west of the meridian — the difference or 
sum will be the right ascension of the meridian, from which (in- 
creased by twenty-four hours if necessary for the purposes of 
subtraction) subtract the sun's corrected right ascension, and 
the remainder will be the astronomical apparent time at ship. 
To this apply the corrected equation of time (see Equation of 



THE NAVIGATOR'S POCKET-BOOK 97 

Time) according to heading of the almanac column and the 
answer will be the astronomical mean time at ship ; then 
the difference between this and the astronomical mean time 
at Greenwich will be the longitude in time, which turned 
into degrees (either by the use of Table 7 or by the rule given 
under the head of Arithmetic of Navigation) will be the lon- 
gitude. 

Remarks. — When the astronomical mean time at the ship and 
the astronomical mean time at Greenwich are of different dates, 
it will be necessary to add twenty-four hours to the time of the 
latest date for the purposes of subtraction between them, then 
the answer will be the longitude in time. 

As explained for the sun, the best hour to observe a time 
altitude of a heavenly body is when it is the nearest to the prime 
vertical. (See Prime Vertical.) 

If desired, several altitudes of the moon may be observed in 
quick succession and the corresponding times by the chronom- 
eter noted, then the mean of these altitudes and times accepted 
as a base from which to calculate the longitude. As explained 
for the sun, this will eliminate any small error as regards the 
altitude and noting of the time. 

If the log. sine of the time cannot be matched, correct the time 
given in the p.m. column according to the rule given under the 
head of Logarithms. 

Longitude by One Altitude of a Planet. — This problem is to 
be worked in the same way as the one described immediately 
preceding for the moon, simply substituting the planet's polar 
distance and right ascension, as may be seen by the following 
rule : 

Add together the planet's corrected altitude, the latitude by 
dead-reckoning, and the planet's polar distance ; divide by 2 
7 



98 the navigator's pocket-book 

and from the half-sum subtract the corrected altitude ; select 
from Table 44 the logs, secant of latitude, cosecant of polar dis- 
tance, cosine of half-sum, and sine of remainder ; add these four 
logs, and divide by 2, calling the answer the sine of a time, 
which take out in the p.m. column, Table 44, and apply said 
time to the planet's corrected right ascension, subtracting it if 
the planet is east of the meridian, but adding it if the planet is 
west of the meridian— the difference, or sum, will be the right 
ascension of the meridian, from which (increased by twenty- 
four hours if necessary for the purposes of subtraction) subtract 
the sun's corrected right ascension and the answer will be the 
astronomical apparent time at the ship, to which apply the cor- 
rected equation of time, then find the difference between this 
astronomical mean time at ship and the astronomical mean time 
at Greenwich ; the answer will be the longitude in time, which 
convert into degrees. 

Longitude by One Altitude of a Star. — As explained for a 
planet, this problem is worked in the same manner as the moon, 
it simply being necessary to substitute the star's polar distance 
and right ascension ; but it is to be explained that corrections 
for the declination and right ascension of stars are too small to 
be considered, simply accepting the same for the given year 
being all that is necessary. (See Fixed Stars.) 

Longitude by Dead-Reckoning. —(See Dead-Reckoning.) 
Longitude by the Artificial Horizon. — (See Artificial Hori- 
zon.) 

LONGITUDE IN ARC— The position or distance of a 
vessel east or west of a given prime meridian, expressed in 
degrees, minutes, and seconds of angular measure. 

LONGITUDE IN TIME.— The position or distance of a 



THE NAVIGATOK'S POCKET-BOOK 99 

vessel east or west of a given prime meridian, expressed in hours, 
minutes, and seconds of time measure. 

LOST DAY.— (See Circumnavigator's Day.) 

LOWER LIMB.— (See Upper Limb.) 

LOWER TRANSIT.— The passage of a heavenly body over 
the meridian 180° distant from the meridian of the upper transit. 
In high northern and southern latitudes at certain times of the 
year the sun and moon do not set during the twenty-four hours, 
but circle around the heavens, at all times in view of the ob- 
server ; consequently they are then seen at the period of their 
lower as well as upper transit. The Xautical Almanac gives the 
astronomical times of the upper transit of heavenly bodies, which 
takes place when the bodies are moving (apparently) from east to 
west. (See Upper Transit ; Midnight Sun.) 

LOW LATITUDES.— Parallels in the vicinity of the equa- 
tor. (See High Latitudes.) 

L'S OF NAVIGATION.— Lead, Lights, Lookout, Latitude, 
Longitude. 

LUBBER'S POINT.— The vertical black line painted on 
the inside surface of the compass bowl, and which represents 
the ship's head and the line of the keel. 

LUNAR. — Relating to the moon. 

LUNAR DAY. — The interval of time between two successive 
transits of the moon over the same meridian. 

LUNAR DISTANCE.— The angular measurement of the 
moon from another heavenly body. 

LUNAR INEQUALITY.— A variation in the moon's mo- 
tion which depends upon its distance from the sun. 



100 THE NAVIGATOR'S POCKET-BOOK 

MAGNET.— An ore that attracts iron. The properties of a 
magnet are that, with the exception of the oxides, it attracts 
iron in all of its various states. If a bar of steel is charged with 
magnetism, either by a magnet or by a dynamo, then suspended, 
horizontally balanced by a slender thread, the bar will indicate 
the magnetic meridian. What is known as an artificial magnet 
is a bar or mass of iron or steel into which the magnetic prop- 
erty has been introduced by the presence of, or contact with, a 
body possessing the same. 

MAGNETIC. — Having power to attract iron. 

MAGNETIC AMPLITUDE.— The bearing by compass of 
a heavenly body at rising and setting, or an arc of the horizon 
intercepted between the body in its rising and setting and the 
east and west compass points. 

MAGNETIC AZIMUTH— The arc of the horizon inter- 
cepted between the vertical circle and the magnetic meridian, 
or the bearing by compass of a heavenly body, calculated from 
the north point in north latitudes and the south point in the 
southern hemisphere. 

MAGNETIC BEARING.— A bearing according to the 
compass, or the direction pointed out by the magnetic needle. 

MAGNETIC DIP. — A property belonging to the magnetic 
needle, whereby one of its poles (ends) inclines toward the 
earth, while the other pole is repelled or elevated. 

MAGNETIC EQUATOR.— A line passing through those 
points on the surface of the earth where the dipping needle rests 
in a horizontal position. (See Compass.) 

MAGNETIC INDUCTION.— Communication of magnetism 
from a magnet to a body of steel in its vicinity, although per- 



THE NAVIGATOR'S POCKET-BOOK 101 

haps not touching it. The communication of magnetism from 
the earth (which is a huge magnet in itself) to the hulls of iron 
and steel vessels is known as the earth's induction. 

MAGNETIC MERIDIAN.— A vertical circle in the heav- 
ens which intersects the horizon in the magnetic poles ; or it may- 
he defined as the natural direction pointed out by the compass 
needle when allowed to turn freely and removed from the effects 
of deviation and local attraction. 

MAGNETIC NEEDLE.— The slender piece of magnetized 
steel to which the compass card is fastened. 

MAGNETIC POLES — Two places on the earth's surface 
where the dipping needle assumes apposition perpendicular to 
the horizon and shows a dip of 90°. The north magnetic pole is 
situated on the parallel of 70° north and on the meridian of 97° 
west ; the south magnetic pole on the parallel of 70° south and 
on the meridian of 145° east. 

MAGNITUDE. — According to their brilliancy the stars are 
classed as of the first, second, third, fourth, fifth, sixth, and 
seventh magnitudes. Stars beyond the seventh magnitude can- 
not be seen with the unaided eye, and are known as telescopic 
stars. 

MAKING THE LAND.— A landfall ; to obtain the first 
view of land. 

MAST-HEAD ANGLES.— To measure the distance between 
the observer's ship and another vessel, it is only necessary to 
know the height of her mast or smoke-stack, and the vertical 
angle of the same measured to the surface of the water — to her 
water-line. If the image of the truck, or the rim of the smoke 
funnel is thrown to the water-line by the sextant, and this angle 



102 THE NAVIGATOR'S POCKET-BOOK 

referred to the danger-angle tables in the back of this book, the 
distance of the vessel will at once be obtained by simple inspec- 
tion. 

To tell, when in a race, if the distance between two vessels is 
increasing or decreasing, note several mast-head angles. If the 
angles increase it proves that the two vessels are drawing nearer, 
but if the angles decrease the vessels are separating more and 
more. (See Danger- Angle Tables.) 

MAST-HEAD COMPASS.— A compass hung at the lower- 
mast-head so as to remove it out of the influence of the magnet- 
ism in the ship's iron. (See Elevator Compass.) 

MEAN NOON. — The time that the mean sun is supposed to 
cross the observer's meridian. 

MEAN SOLAR TIME — Time calculated by the motion of 
the mean sun. All watches and clocks represent mean solar 
time. 

MEAN SUN. — An imaginary sun which is supposed to 
move uniformly and to cross the same meridian the same time 
every day, thus giving a value of exactly twenty-four hours to 
the day. This mean or fictitious sun sometimes crosses the 
observer's meridian a little in advance of the true sun, and at 
other times a little after it, and this difference or interval between 
the real and imaginary suns is known as the equation of time. 

By referring to the almanac it will be seen that four times in 
each year the real and imaginary suns pass the same meridian at 
the same time ; namely, about April 14th, June 13th, August 
31st, and December 23d ; consequently on these days the equa- 
tion of time may be considered as zero. The maximum equa- 
tion of time is about 16 m. 20 sec. 



THE NAVIGATOR'S POCKET-BOOK 103 

MEAN TIMS. — Same as mean solar time. 
MERCATOR'S CHART.— (See Chart.) 

MERCATOR'S SAILING.— A method of finding (indepen- 
dent of the parallel rules and dividers) the true course and dis- 
tance between two places by employing meridional parts instead 
of the middle latitude. 

Rule. — Find the difference of latitude and the difference of 
longitude between the two places. If the two latitudes have 
the same name (both north or both south) subtract one from 
the other, but if they have different names add them together. 
Now multiply the degrees of the answer by 60 to convert them 
into miles and add in the minutes as they represent miles ; the 
answer will be the difference of latitude. Proceed to find the 
difference of longitude in the same way — add the longitudes to- 
gether if of different names, but subtract between them if of the 
same name. 

Turn to Table 3 and select the meridional parts for the degrees 
and minutes of each latitude, and if the latitudes are of differ- 
ent names, add the meridional parts, but if the latitudes are of 
the same name, subtract one of the meridional parts from the 
other. In other words, if the latitudes were added the me- 
ridional parts must be added, and if the latitudes were subtract- 
ed the meridional parts must be subtracted. 

With the meridional difference of latitude and the difference 
of longitude turn to Table 2 and make them compare by seeking 
in the latitude column for the meridional difference of latitude 
and in the departure column opposite for the difference of longi- 
tude. On the page of their comparison the true or geographical 
course between the two places will be read in degrees from the 
top of the page if the meridional difference of latitude is greater 



104 THE NAVIGATOR'S POCKET-BOOK 

than the difference of longitude, but it will be read from the 
bottom of the page if the difference of longitude exceeds the 
meridional difference of latitude. 

On the same page apply the proper difference of latitude in 
the latitude column from that part of the page (top or bottom) 
where the course was read, and opposite to the left in the dis- 
tance column will be found the distance in nautical miles for 
the course found, which, in other words, will be the number of 
miles required to be sailed on a direct line between the ship's 
place and the point sought. 

The variation (also the deviation, if any exists) of the compass 
must be applied to the true course in order to convert the same 
into a magnetic course, or the course necessary to be steered by 
the ship's compass in order to make the true track. 

To Apply Variation. — Suppose the true course found is 
southeast, and the chart informs us that in the ship's locality 
there is one point of westerly variation. The effect of this is 
that the southeast point of the compass is swung so that it really 
points southeast -by-east, and in order to make a true southeast 
course the ship must be steered southeast-by- south according 
to the compass. 

Rule. — A simple rule to remember for converting a true 
course into a magnetic course is to allow westerly variation 
away from the true course in the direction that the hands of a 
watch revolve, and easterly variation contrary, or against the 
hands of a watch. 

To Apply Deviation. — If deviation exists for the magnetic 
course found, the latter must have the deviation applied to it on 
exactly the same principle as explained for variation. For ex- 
ample, we will say that the magnetic course found is southeast- 
by-south, and that there is one point of westerly deviation to be 



THE NAVIGATOR'S POCKET-BOOK 105 

allowed for when the ship's head is on that course. The com- 
pass course to be steered in this case is south-southeast, in order 
to make a correct magnetic course of southeast-by-south. 

Remarks. — The variation must always be applied before 
applying the deviation. 

It is to be remembered that the compass course must be re- 
shaped as often as the variation changes. For example, we will 
say that the true course from Sandy Hook to Bermuda Island is 
S. 42° E., and that in the vicinity of Sandy Hook the variation 
of the compass is 8° westerly. The magnetic course in this case 
is S. 34° E., which equals southeast-by-south. To this course 
we apply the deviation correction (if any exists) given by our 
deviation card or found by observation, and then we hold the 
indicated compass course until we reach a latitude and longitude 
where the variation of the compass is shown to change, when it 
becomes necessary for us to apply the new variation given by 
the chart and change the course accordingly. 

When, by reason of opposing winds or other causes, the vessel 
does not keep on the direct course for the port bound to, then 
the whole process of laying out the course must be gone through 
with again. This may happen many times before the port is 
reached. 

Mercator's Sailing is to be preferred to Middle Latitude Sail- 
ing, unless the course is nearly east or west. 

MERCURIAL BAROMETER. — An instrument which 
shows the pressure of the air or weight of the atmosphere. It 
is a tube thirty-four inches long, closed at the top and exhausted 
of air. The lower end of this tube is immersed in a cup or 
cistern of mercury, and the pressure of the atmosphere causes 
the fluid to ascend in the slender, hollow column. The varia- 
tion in height of the mercury is dependent upon the weight or 



106 THE NAVIGATOR'S POCKET-BOOK 

pressure of the atmosphere. These variations are measured by- 
aid of a scale graduated in inches and parts and fixed against 
the tube. When the mercury in the cistern is pressed down 
by the air the mercury rises in the exhausted tube, but when 
the mercury in the cistern rises on account of diminished press- 
ure of air the mercury in the tube falls. (See Barometer.) 

MERIDIAN. — The highest point of the great arc described 
by a heavenly body from its rising to its setting. When the 
sun crosses the observer's meridian it is 12 o'clock, apparent 
noon, at his place. A meridian is an imaginary great circle of 
the sphere extending from pole to pole. (See Circumnavi- 
gator's Day ; Prime Meridian ; Secondary Meridians ; Tertiary 
Meridians. ) 

MERIDIAN ALTITUDE.— The angular height of a heav- 
enly body from the horizon line at the time the body is crossing 
the meridian. (See Altitude ; Latitude.) 

MERIDIAN PASSAGE.— The crossing of a heavenly body 
over the meridian of the observer. (See Lower Transit ; Upper 
Transit.) 

MERIDIAN SAILING.— Sailing on a meridian ; sailing 
true north or south. (See Parallel Sailing.) 

MERIDIONAL DIFFERENCE.— The quantity given in 
Table 3, which bears the same proportion to the difference of 
latitude that the difference of longitude bears to the departure. 

MERIDIONAL FARTS.— Degrees of latitude increased 
from their natural lengths more and more as the equator is 
receded from, and the lengths of the small portions of the 
meridian thus increased, expressed in minutes of the equator, 
are called meridional parts. (Table 3.) 



THE HAVIGATOR's POCKET-BOOK 107 

METEOROLOGY.— The science of the atmosphere and its 
phenomena. (See Log-Book ; Weather.) 

MIDDLE LATITUDE.— Half of the sum of two latitudes 
of the same name, but half of the figures left after subtracting 
between two latitudes of different names. The middle latitude 
between 20° north and 30° north is 25° north. The middle lati- 
tude between 20° north and 30° south is 5° south. 

MIDDLE-LATITUDE SAILING— The method of finding 
(independent of the parallel rules and dividers) the true course 
and the distance between two places by employing the middle 
parallel between them. 

Rule. — Find the difference of latitude and the difference of 
longitude between the two places. If the two latitudes have 
the same name (both north or both south) subtract one from the 
other ; but if they have different names add them together. 
Now multiply the degrees of the answer by 60 to convert them 
into miles, and add in the minutes as they represent miles ; the 
answer will be the difference of latitude. Proceed to find the 
difference of longitude in the same way : add the longitudes to- 
gether if of different names, but subtract between them if of the 
same name. 

Next, to find the middle latitude : if the two latitudes are of 
the same name add them together and divide by 2 ; but if they are 
of different names subtract one from the other and divide by 2. 
The answer will be the parallel equidistant between the place 
of the ship and the port sought. 

With this middle latitude turn to Table 2, and on the page 
marked with the degrees of the middle latitude apply the dif- 
ference of longitude in the distance column, and opposite to the 
right in the latitude column (reading from the top of the page if 



108 THE NAVIGATOR'S POCKET-BOOK 

the degrees were found there, but from the bottom of the page 
if the degrees were found there) will stand the departure, or the 
number of nautical miles in an east and west line between the 
ship and the sought-for port. 

K"ow, with the difference of latitude and the departure make 
them compare in Table 2 in their respective columns opposite 
one another, and in the distance column to the left will be seen 
the direct distance to be sailed in nautical miles, and the true or 
geographical course between the two places will be read in de- 
grees from the top of the same page if the difference of lati- 
tude is greater than the departure, but the course will be read 
from the bottom of the same page if the departure exceeds the 
difference of latitude. 

The variation (also the deviation, if any exists) of the compass 
must be applied to the true course in order to convert the same 
into a magnetic course, or the course necessary to be steered by 
the ship's compass, in order to make the true track. 

To Apply Variation. — Suppose the true course found is 
south and the chart informs us that in the ship's locality there 
is one point of easterly variation. The effect of this is that the 
compass south point is swung so that it really points south-by 
west, and in order to make a true south course we must steer 
south-by-east by the compass. 

Rule. — A simple rule to remember for converting a true course 
into a magnetic course is to allow the amount of westerly varia- 
tion away from the true course in the direction that the hands 
of a watch revolve, and easterly variation contrary or against 
the hands of a watch. 

To Apply Deviation. — If deviation exists for the magnetic 
course found, the latter must have the deviation applied to it on 
exactly the same principle as explained for variation. For ex- 



THE KAVIGATOK^S POCKET-BOOK 109 

ample, we will say that the magnetic course found is northeast, 
and that there is half a point of westerly deviation to be allowed 
for when the ship's head is on that course. The compass course 
to be steered in this case is northeast-half-east, in order to make 
a correct magnetic course of northeast. 

Remarks. — The variation must always be applied before ap- 
plying the deviation. 

It must be borne in mind that the compass course is to be re- 
shaped as often as the variation changes. For example, we 
will say that the true course found is N. 45° E., and that in the 
locality of the ship the variation of the compass is 6° easterly. 
The magnetic course in this case is N. 39° E., which equals 
northeast half-north. To this course we apply the deviation 
correction (if any exists) given by our deviation card or found 
by observation, and then we hold the indicated compass course 
until we reach a latitude and longitude where the variation of 
the compass is shown to change, when it becomes necessary 
to apply the new variation given by the chart, and change the 
course accordingly. 

When by reason of head winds or other causes the vessel 
does not keep on the direct course for the port to which she is 
bound, then the whole process of laying out the course must be 
gone through with again. This may occur many times before 
the port is reached. 

Middle-Latitude Sailing is to be preferred to Mercator's Sail- 
ing when the course is nearly east or west. 

MIDDLE POINT.— (See Drift.) 

MIDNIGHT SUN.— As explained under the head of Lower 
Transit, in high latitudes during the summer season there are 
times when the sun does not set for the observer during the 



110 THE NAVIGATOR'S POCKET-BOOK 

twenty-four hours, and on account of crossing at 12 o'clock at 
night the meridian 180° distant from the meridian which it 
crossed when it made its upper transit, it derives its name of 
the midnight sun. 

MILE. — A statute mile is 5,280 feet ; a nautical or geograph- 
ical mile 6,082.66 feet ; the latter is also called a knot. 

MINUTE. — A mile of latitude and a minute of latitude are 
of equal value — 6,082.66 feet. A minute of longitude varies 
in value according to the distance from the equator. At the 
equator a minute of longitude is equal to a minute of latitude. 
On the parallel of 60° north or south a minute of longitude is 
equal to only half a minute of latitude. Longitude value de- 
creases in proceeding from the equator toward the poles, where 
it is lost, all the meridians converging to a point ; consequently 
neither the north nor south poles possess longitude. 

MINUTE OF ARC. — A minute of angular measure ; a 
minute measured on the sextant. 

MIRROR. - (See Sextant.) 

MIXED TRACE.— (See Great-Circle Sailing.) 

MOON. — An opaque celestial body receiving its light from 
the sun ; mean distance from the earth 238,800 miles ; diameter 
2,160 miles ; mean apparent diameter 32'. 

MOON CULMINATING STAR.— A star that crosses the 
meridian at the same time that the moon makes its transit. 

MORNING STAR. — When a planet rises before the sun it 
is called the morning star, and when it appears in the western 
sky shortly after sunset it is called the evening star. 

NADIR. — The point of the heavens vertically under the ob- 
server's feet. The nadir is diametrically opposite to the zenith. 



THE NAVIGATOR'S POCKET-BOOK 111 

NATIONAL OBSERVATORY.— An astronomical estab- 
lishment situated in the capital city of a nation. The meridian 
which passes through the observatory is accepted as the first or 
prime meridian of that country. (See Prime Meridian.) 

NAUTICAL ALMANAC— (See Almanac.) 

NAUTICAL ASTRONOMY. — That part of astronomy 
which is used for determining the latitude and longitude of the 
ship by calculations of the sun, moon, and stars. Amplitudes 
and azimuths also belong to nautical astronomy. 

NAUTICAL DAY.— Same as sea day. 

NAUTICAL MILE.— (See Mile.) 

NAUTICAL STARS.— Certain bright stars tabulated in the 
Nautical Almanac, used by navigators for determining the ves- 
sel's position. The principal ones are given in the star tables in 
the back of this volume, and under the head of Fixed Stars. 
(See Latitude.) 

NAUTICAL TABLES.— Specially computed tables for the 
solution of navigation problems. Bowditch's tables, published 
by the United States Government, are accepted by the naval au- 
thorities of all nations as standard, although England, France, 
and other countries have their own tables. Bowditch's tables 
are the ones referred to throughout the text of this work. 

NAVIGATING COMPASS.— The standard compass. 

NAVIGATION. — The science of locating the position of a 
ship at sea, and conducting a vessel from one port to another. 

NEUTRAL POINT. — A magnet in the shape of a steel bar 
has a north polarity at one end and a south polarity at the other. 
The middle of the bar is totally devoid of magnetism, and this 
space is called the neutral point. 



112 THE NAVIGATORS POCKET-BOOK 

NOCTURNAL.— Relating to the night. 

NOCTURNAL ARC— The fire described by a heavenly 
body from its setting to its rising. 

NODE. — When a planet crosses from north to south it is in 
the descending node, and when it crosses from south to north it 
is in the ascending node. 

NOON. — When the centre of the real sun is on the observer's 
meridian it is apparent noon not only with him but at all places 
on his meridian from pole to pole. (See Mean Sun ; Siderial 
Noon.) 

OBJECT-GLASS.— The lens situated in the large end of a 
telescope, the same being the first to receive the image or rays 
of light. 

OBSERVATION.— To determine the angular height of a 
heavenly body above the horizon for the purpose of calculating 
the ship's position. 

OCCULTATION.— The eclipse of one heavenly body by 
another. 

OCTANT. — A nautical instrument of reflection for measuring 
altitudes of heavenly bodies. It is constructed on the same 
principles as the sextant, but of more limited arc and graduated 
to only 15" instead of 10". The metal-frame and silver-arc oc- 
tant with an arc reading to about 120° is a much superior instru- 
ment in every way to the quadrant. The manner of adjusting 
and using the octant is identical with that of the sextant, conse- 
quently it would be repetition to treat the subject under this 
head, and the reader is referred to the rules given under the 
head of Sextant. Some old-fashioned octants are cut to 20" of 
arc and others even to 30". (See Quadrant ; Sextant.) 



THE NAVIGATOR'S POCKET-BOOK 113 

OFF THE ARC— (See Sextant.) 

OIL COMPASS. — A liquid compass ; a compass in which 
the card floats about in oil instead of a mixture of alcohol and 
water. (See Liquid Compass.) 

ON THE ARC— (See Sextant.) 

OPPOSITION.— When a heavenly body is 180° of longitude 
distant from the sun it is said to be in opposition. 

ORBIT.— The imaginary path described by a heavenly body 
in its revolution ; the track of a planet round the sun. 

P.M. — Post Meridiem ; after meridian ; embraces the twelve 
hours from noon to midnight. 

PARALLAX. — The apparent displacement of a heavenly 
body as seen from two different stations. The sun's parallax is 
shown in Table 16 ; the moon's parallax (less refraction) in Table 
23, and the parallax of the planets in Table 17. (See Corrected 
Altitude ; Horizontal Parallax.) 

PARALLEL RULES.— Two flat rules connected with piv- 
oted cross-hinges so that the rules may remain parallel when 
spread out. They are used for shaping courses and determining 
bearings on the chart. 

PARALLELS.— Circles of latitude parallel to the equator. 

PARALLEL SAILING.— Sailing on a parallel ; sailing true 
east and west. (See Meridian Sailing.) 

PARHELIA. — A mock sun ; an image of the sun which is 
occasionally seen close to and at the same height above the hori- 
zon as the true sun. 

PASSAGE.— (See Meridian Passage.) 

PATENT LOG. — An instrument for measuring the distance 
8 



114 THE NAVIGATOR'S POCKET-BOOK 

(in nautical miles) run by a vessel. It consists of a register, 
rotator, and line, the latter connecting the two metal parts. The 
rotator is towed astern, and by its revolutions turns the line com- 
municating with the register and turns the dial hands within. 

To Rig the Log. — Pass the log-line through the long fore-and- 
aft hole in the rotator and make a small Flemish eye in the end of 
the line ; then sew a piece of leather for chafing gear around that 
part of the line which rubs against the small or forward end of 
the rotator. Next secure the Flemish eye to the after-part of the 
rotator by the wooden or metal peg furnished, and fasten the 
hook to the other end of the line by a couple of half-hitches. 
Secure the indicator so that it will ride freely on the tafTrail, 
permitting the angle of the indicator bar to correspond with the 
angle of the line, thus preventing undue friction upon the shaft- 
bearing when the log is being towed. Give line to the rotator 
according to the freeboard and speed of the vessel. A very high 
freeboard, or a steamer making more than ten knots, will require 
all the line furnished to prevent the rotator from skipping, 
whereas a low freeboard or a vessel making anywhere from five 
to ten knots will require about two-thirds of the line. 

To Read the Dial. — Some registers have two and some three 
dials. In the latter case the first one is marked in quarters, each 
division representing one-quarter of a mile ; the second in even 
miles, recording as high as ten ; the third in ten-mile divisions, re- 
cording as high as one hundred. When the ship has sailed one 
hundred miles, the three hands all point at zero, and at such 
time a suitable memorandum is made in the log-book, so that 
the record may be faithfully preserved. Where the register has 
onl} T two dials, one of them represents quarter miles and the 
other single-mile divisions extending to one hundred. 

Remarks. — When a vessel's speed exeeeds eighteen miles an 



THE NAVIGATOR'S POCKET-BOOK 115 

hour, the majority of patent logs are of little value, as they will 
not record correctly the distance run by the vessel on account of 
skipping. If sufficient line is given them to overcome this skip- 
ping and attendant loss, they will be too sluggish to render an 
honest return. In such cases recourse is had to the chip log, 
and the rough distance run is also calculated by dividing the 
number of revolutions made by the propeller by the number 
allowed for one mile. 

To Allow for Current. — When a ship is sailing with or against 
a current, the velocity of same must be taken into account and 
applied either as a plus or minus quantity to the reading of the 
dial. 

Examples. — According to the register, the vessel heading west 
has made ten miles in the past hour, but it is known that during 
that time the ship has been in a current flowing west at the rate 
of two miles an hour ; consequently this two miles must be added 
to the reading of the register, making the corrected distance run 
twelve miles. 

The register shows that during the past hour the vessel head- 
ing south has made ten miles, but it is known that during 
that time the ship has been in a current setting north at 
the rate of two miles an hour ; consequently this two miles must 
be subtracted from the reading of the register, making the cor- 
rected distance run only eight miles. 

Explanation. — When a vessel is going neither directly with 
or against a current, but sailing a course that makes an angle 
with it, then it becomes a calculation of current sailing, and 
must be considered in the manner explained under that head. 

PATTERSON'S METHOD.— (See Chart Sailing.) 

PELORUS. — An instrument much used for observing bear- 



116 THE NAVIGATOR'S POCKET-BOOK 

ings and for finding the deviation of the compass, taking the 
place of the azimuth attachment, shadow-pin, etc. It consists of 
a circular dial of brass graduated with the points and degrees of 
the compass, and two upright arms which revolve around the 
circle. This plate is hung in gimbals so that it will preserve a 
horizontal position when the vessel pitches and rolls. One of the 
uprights is fitted with a perpendicular thread running its length, 
also a small hinged mirror at its base, and the other upright is 
provided with a colored eye-screen which is made to slide up 
and down the length of the arm, and is for the purpose of pro- 
tecting the eye from the glare of the sun when taking a bearing 
of that body. A mark on the inner gimbal ring indicates the 
line of the keel or the ship's head, and a clamp screw admits of 
the dial being secured against turning after it has been set. 

Pelorus Stands. — Suitable stands for the pelorus should be 
provided on different parts of the deck, in order that bearings 
may be taken at any station by simply carrying the pelorus to it 
and setting it on its stand. The idea of this is that if the view is 
obstructed (by a mast, funnel, sail, or deck-house) from one 
point, another may be selected which will give a clear field. It 
is recommended that steamships have stands built on each end 
of the bridge and on each quarter. These stands require to be 
but simple shelves hinged to the rail and provided with raised 
strips or coamings of wood running round them for the pelorus 
box to snugly set into and to protect the same from rolling off. 
The stands must have their fore-and-aft coamings parallel to the 
ship's keel, so that when the pelorus box is placed, the zero line 
of the card will coincide with the line of the keel. The man- 
ner of effecting this is explained in the following : 

The ship being on an even keel while in dock or at anchor in 
the stream, set the pelorus square on one of the shelves, with the 



THE NAVIGATOR'S POCKET-BOOK 117 

lubber's mark forward, and measure carefully the distance from 
the centre of the instrument to the midship seam of the deck, 
then lay off toward the bulwarks from this seam a conspicuous 
mark on the forward deck (on the side that the instrument is on) 
the same distance as exists between the pelorus and the seam. 
Next set the zero point of the pelorus dial to the lubber's mark 
on the gimbal ring, and observe that the sight-vanes are placed at 
zero. Look forward through the sight-vanes at the mark erected, 
and move the box one way or the other until the mark is seen 
to be cut by the thread. Now secure the coamings on the lines 
indicated by the box, and proceed in a like manner for each one 
of the shelves. 

To Take a Bearing. — Set the pelorus to the course of the 
ship according to the standard or navigating compass, then so 
long as the ship is held steady on said course, any bearings taken 
by the pelorus will represent the magnetic bearing of the object 
exactly the same as though it had been observed directly from 
the standard compass itself. 

In order to find the deviation of any particular compass, simply 
set the pelorus to the course of the ship as shown by that com- 
pass, and proceed to take the sun's bearing and work out the am- 
plitude or azimuth. (See Amplitude ; Azimuth.) 

PERMANENT MAGNETISM.— An artificial steel magnet 
will part with a little of its original strength after being charged, 
the balance contributing what is known as its saturation point, 
which it will retain for many years without appreciable loss, 
and is known as permanent magnetism. 

PERPENDICULAR.— A line at right angles to the plane of 
the horizon ; a plumb-line ; a line at a right angle to the base. 

PERSONAL EQUATION.— The difference in judgment 



118 THE NAVIGATOR'S POCKET-BOOK 

shown between two observers in measuring an altitude of the 
same object, etc. 

PLANE. — A level surface. In astronomy planes are ideal 
and pass through certain points of the heavens — planes of the 
horizon, equator, etc. 

PLANE CHART. — A chart representing the earth's surface 
as a plane. 

PLANE SAILING, — Calculating courses, etc., on the sup- 
position that the surface of the earth is a plane. 

PLANET. — An opaque celestial bod}% which, like the moon, 
receives its light from the sun. The nine principal planets are 
Mercury, Venus, Earth, Moon, Mars, Jupiter, Saturn, Uranus, 
Neptune. (See Fixed Stars.) 

PLANISPHERE.— A chart of the heavens. 

PLOTTING. — To plot the latitude and longitude of a vessel 
is to trace on a chart the courses and distances made. Where 
the last line ends will be the ship's place. It is a modification of 
dead-reckoning. 

POINT. — One of the thirty-two divisions of the compass card ; 
exact place ; station. 

POINTERS.— The two stars in the ladle of the Dipper that 
point out the North Star. (See Dipper.) 

POLAR CIRCLES.— The two parallels situated 23° 28' from 
the poles of the earth. (See Antarctic Circle ; Arctic Circle.) 

POLAR DISTANCE. — The angular distance of a heavenly 
body from the elevated pole, the same being found by either 
adding its declination to or subtracting it from 90°. Polar dis- 
tance is reckoned from the pole that is in the hemisphere of the 
observer. For example, if the observer is in north latitudes, the 



THE NAVIGATOR'S POCKET-BOOK 119 

angular distance of the body would be figured from the ele- 
vated north pole, and if the observer was in the southern hemi- 
sphere, it would be measured from the south pole. 

Examples. — An observer situated north of the equator wishes 
to know the sun's polar distance. The declination of the body 
is 10° north ; consequently the sun's north polar distance is 80°. 

An observer situated south of the equator requires the moon's 
polar distance. The declination of the body is 20° north ; con- 
sequently the moon's south polar distance is 110°. 

POLARIS.— The Pole or North Star. It is a star of the sec- 
ond magnitude in the tail of the Little Bear. Polaris is only 
about li° from the pole, and its altitude is always the approxi- 
mate latitude of the observer. When Polaris is at its greatest 
distance from the meridian its altitude is practically the same as 
the elevation of the pole, which is equal to the latitude of the ob- 
server. Polaris is calculated to be two hundred and ninety- two 
millions of miles from the earth. Polaris is approaching the 
pole, and in a hundred and twenty years from now it will be 
about 30' from it, after which it will commence to recede. These 
changes arise from the precession of the equinoxes. The annual 
variation of the declination of Polaris is 19" ; in other words, 
it is approaching the pole at the rate of 19" yearly. 

POLE COMPASS. — A. compass that is elevated above the 
deck by means of a long, stout pole. Access is had to the in- 
strument by a ladder fixed permanently between the deck and 
the top of the pole. The compass is so situated to remove it 
beyond the disturbing influences of the ship's iron. 

POLES. — The extremities of the earth's axis ; the two points 
on the earth's surface 90° distant from the equator. (See Mag- 
netic Poles.) 



120 THE XAVIGATOR'S POCKET-BOOK 

POSITION.— Relating to the place of the ship. 

PRECESSION OF THE EQUINOXES.— The equinoctial 
points do not preserve a constant place among the stars, but 
move backward, or toward the west, along the ecliptic at the 
annual rate of 50"; consequently a complete revolution occu- 
pies 25,868 years. The precession is caused by the unequal at- 
traction of the sun and moon on the equator, combined with the 
earth's rotation on its axis. 

PRICKING POSITION.— With the dividers take from the 
graduated meridian on the side of the chart the given latitude 
and mark this on the meridian the nearest to the given longitude ; 
then lay the bevelled edge of the parallel rules on a near parallel 
and slide them along to the point marked on the meridian. Now 
with the dividers take the given longitude from the graduated 
parallel and lay this down along the edge of the parallel rules, 
and this will define the ship's latitude and longitude. 

PRIMARY MERIDIAN.— Same as Prime Meridian. 

PRIME MERIDIAN.— The starting-point of longitude. 
The first meridian of a country established by the situation of its 
national observatory. Longitude is counted east and west from 
the first meridian up to 180°. The French use the meridian of 
Paris as a first meridian ; the English that of Greenwich ; the 
Russians that of St. Petersburg ; the Americans that of Wash- 
ington, etc. For convenience, American navigators (and others) 
also use the meridian of Greenwich, as it permits them to navi- 
gate by English charts, many of the same representing parts of 
the world of which we have no survey of our own. For pur- 
poses of navigation, a chronometer must be regulated to the 
prime meridian of the country whose chart is used — if a French 
chart is employed, the chronometer must be set to Paris time ; 



THE NAVIGATOR'S POCKET-BOOK 121 

if an English chart is used, the chronometer must represent 
Greenwich time, etc. (See Circumnavigator's Day ; Secondary 
Meridians.) 

PRIME VERTICAL. — The vertical circle passing through 
the east and west points of the horizon. A heavenly body is in 
or on the prime vertical when it hears true east or true west — 
when it is at right angles to the meridian. When a body is ob- 
served on the prime vertical for the purpose of calculating the 
longitude, a considerable error in the latitude by dead-reckon- 
ing (used in the computation) will not appreciably affect the re- 
sult. By this it will be understood that the best time to observe 
a longitude sight (be it sun, moon, planet, or star) is when the 
body is on the prime vertical ; but it is to be explained that it 
is not always possible to obtain such an observation, for a heav- 
enly body can only bear true east or true west when its declina- 
tion is of the same name as the ship's latitude and less than the 
latter. When the declination of the body is of the same name 
but greater than the ship's latitude, the body's nearest approach 
to the prime vertical will be some time after it has risen ; but 
when the declination is of a contrary name to the latitude, the 
body will be the nearest to the prime vertical at its rising and 
setting. By referring to a set of azimuth tables the navigator 
will be able by mere inspection to determine the hour and min- 
ute that the body will be on or will approach the nearest to the 
prime vertical. All that is necessary is to refer to the page show- 
ing the ship's latitude and the declination, then run down the 
latter column until the closest figures to 90° are obtained, and 
look opposite in the side column for the time. When the dec- 
lination and the latitude are nearly the same, the sun will be 
nearest the prime vertical a short time before and after its merid- 



122 

ian passage, consequently at such times a very high altitude 
may be employed for finding the longitude of the ship. 

PRISMATIC ATTACHMENT.— A small portable instru- 
ment fitted with a prism-glass, so adjusted on top of the com- 
pass glass that the bearing of an object may be read from the 
compass card by reflection. 

PROJECTIONS.— Charts ; maps ; delineations. 

PROTRACTOR. — An instrument for measuring angles. 
(See Course Protractor.) 

QUADRANT. — A navigating instrument of reflection used 
for measuring angles. It is on the same principle as the octant 
and sextant, but inferior in construction and graduated only to 
1* of arc. 

Description of the Quadrant. — The quadrant contains an arc 
of 45°, but owing to its double reflection it measures 90°, read- 
ing from right to left. The arc is divided into degrees, and 
these are subdivided into three parts of twenty minutes each, 
and the vernier on the sliding limb is divided into single min- 
utes. The sliding or index limb is moved from right to left in 
measuring altitudes, and the screw on the back is used for 
clamping it against the arc after the altitude has been roughly 
measured. The screw on the forward part of the limb is called 
the tangent screw (set tangent to the arc) and is used for gently 
moving the sliding limb when it is clamped so as to make a 
perfect contact of the body with the horizon. The colored 
glasses are for shading the e} T e when obtaining an altitude of 
the sun. 

To Read the Altitude. — Ascertain the number of degrees and 
thirds of a degree that the zero on the vernier has passed on the 
arc, then look along the vernier until one of its lines cuts ex- 



THE HAVIGATOH'S POCKET-BOOK 123 

actly with one of the lines on the arc, and the number of min- 
utes given on the vernier will be added to the reading originally 
obtained on the arc — the whole answer being the required alti- 
tude. 

Remarks. — The quadrant is a crude instrument, and is not 
used by good navigators. The metal-frame octant and the sex- 
tant are standard instruments, but on account of the sextant 
affording means of measuring greater angles than the former, it 
is to be preferred to the octant. 

The quadrant is adjusted in the same manner as explained for 
the sextant. (See Octant; Sextant.) 

QUADRANTAL DEVIATION.— The deviation of the com- 
pass arising from the difference of the induced magnetism in 
the thwartships and horizontal iron in the ship, and which is 
corrected by two iron spheres attached to the port and star- 
board sides of the binnacle. These spheres are known as quad- 
ran tal correctors. 

QUADRATURE.— When the moon is 90° from the sun— at 
one of the two points in her orbit equally distant from the con- 
junction and opposition — she is said to be in quadrature. 

RADIUS. — The distance from the centre of a circle to its cir- 
cumference. 

RATE. — The daily variation of a chronometer from the time 
of the meridian to which it is set. The aggregate of the gain or 
loss is respectively subtracted from or added to the face of the 
chronometer in order to obtain the correct Greenwich mean time 
at the instant of observation. 

Sea Rate.— Sometimes the chronometer does not maintain 
when at sea the rate furnished for it by the makers or dealers, 
and which is known as the instrument's shore rate. To as- 



124 

certain the sea rate, take the difference between the chronom- 
eter's error on the day of sailing and the gross error deter- 
mined when the vessel makes port, and the result divided by 
the number of days at sea will be the sea rate. (See Chronom- 
eter.) 

RATIONAL HORIZON.— A plane passing through the cen- 
tre of the earth and parallel to the sensible horizon at the ob- 
server's station. (See Sensible Horizon.) 

READING. — To read an altitude is to observe the height of 
an object recorded on the arc of a sextant, octant, etc. 

RECIPROCAL BEARINGS.— Mutual bearings of the same 
object by two compasses placed in line, one on board and the 
other on shore where it is free from magnetic disturbances in 
the way of local attraction. 

REDUCTION. — To change hours, minutes, and seconds into 
arc, or to change degrees into time. To apply a certain quan- 
tity of arc to an ex-meridian altitude is called reduction to the 
meridian. 

REFRACTION.— The change of direction of a ray of light 
in passing through atmospheric mediums of varying densit} T . 
Refraction is ever a minus correction, and is tabulated in Table 
20 for all heavenly bodies. It is to be explained, however, that 
Table 23 gives the parallax of the moon, less the refraction. (See 
Corrected Altitude.) 

REGULATING. — What is known as regulating a watch or 
clock at sea is simply to correct it so that it will show the local 
apparent time at ship. It is done as follows : Observe an alti- 
tude of the sun as for a regular chronometer sight for rinding 
longitude, and also note the time shown by the ship's clock at 



THE NAVIGATOR'S POCKET-BOOK 125 

the instant ; then proceed to work up the sight by the regular 
rule (see Longitude), and compare the apparent time at ship 
given for the sine of the logarithms with the time shown by the 
clock when the sight was taken ; the difference will be the error 
of the clock, the hands of which will be set back or advanced 
as required. This method is also known as finding the time. 

RESIDUAL ERRORS.— Deviation remaining after the com- 
pass has been adjusted as closely as possible. (See Compass.) 

RETENTIVE MAGNETISM.— When a ship's head has 
been in one direction for a long time either at a dock or on a 
long course at sea, the hull becomes temporarily magnetized in 
a direction parallel to the magnetic meridian, owing to the 
earth's inductive force. Sometimes this magnetism remains for 
several days after the direction of the ship's head has been 
changed, hence its name " retentive." It then gives way to 
magnetism induced in a new direction according to the change 
of course. It is because of this retentive magnetism that the 
deviation card should be continually checked at sea, especially 
upon changing the course. The temporary effect of retentive 
magnetism upon the compass is to cause it to deviate invariably 
in the direction of the last course, hence if a vessel has been 
heading south for several days, and her course is changed to 
west, it will be found that the natural deviation for that point 
has been increased if the deviation has been westerly, and dimin- 
ished if it has been easterly. 

REVOLVING STORM.— (See Law of Storms.) 
RHUMB LINE.— The track of a ship sailing constantly 
toward the same point of the compass ; a line prolonged on a 
nautical chart from any point of the diagram compass. 
RIGHT ASCENSION.— The distance considered in time of 



126 THE NAVIGATOR'S POCKET-BOOK 

a heavenly body reckoned eastward on the equinoctial from the 
First Point of Aries— counted from h. to 24 h. (0° to 360°). 
The First Point of Aries is that point in the heavens which the 
sun's centre occupies at the time of the vernal equinox, when 
the body changes from south to north declinations. Right as- 
cension may be expressed as the celestial longitude of a heaven- 
ly body. The correction for the hourly or minute difference of 
right ascension is found and applied in the same wa}^ as explained 
for the difference of declination. In other words, the right as- 
cension is reduced to the Greenwich time of observation as 
shown by the chronometer, by multiplying the hourly difference 
in the case of the sun and planets, but the minute difference in 
the case of the moon, and then adding this correction to or sub- 
tracting it from the right ascension proper according as the lat- 
ter is increasing or decreasing. 

RIGHT ASCENSION OF THE MERIDIAN.— The angle 
at the pole included between the meridian of the observer and 
the meridian passing through the First Point of Aries. It is 
reckoned eastward in the order of the signs. Sidereal time and 
right ascension of the meridian are one and the same thing. In 
other words, the hour angle of the First Point of Aries is equal 
to the right ascension of the meridian of an observer, which is 
precisely the same thing as sidereal time. 

RIGOROUS METHOD.— Navigation problems calculated 
according to exact principle ; allowing of no abatement ; accu- 
rate in the smallest detail. 

RISING.— The appearance of a heavenly body mounting 
above the horizon. Celestial bodies continue to rise from the 
eastern horizon line until they cross the meridian of the observ- 
er, when they begin to fall. 



THE NAVIGATOR'S POCKET-BOOK 127 

ROUGH LOG.— Same as log slate. 

SAILINGS.— (See Great-Circle, Mercator's, Meridian, Mid- 
dle-Latitude, Parallel, Plane, and Spherical Sailings.) 

SATURATION POINT.— (See Permanent Magnetism.) 

SEA DAY.— The old fashioned way of keeping the date at 
sea was to consider the day and date to commence at noon and 
to end and begin again the following noon, so that the sea clay 
and date began twelve hours before the civil date and twenty- 
four hours before the astronomical date. This ridiculous prac- 
tice belongs entirely to the past. 

SEA RATE.— (See Rate.) 

SECONDARY MERIDIANS— Those connected with the 
prime meridian by exchange of telegraphic time signals. Sec- 
ondary meridians are determined with the utmost degree of care 
in order to locate with accuracy the positions of prominent 
points on the coasts. (See Tertiary Meridians.) 

SEMICIRCULAR DEVIATION.— So called because it has 
the contrary name and maximum value in opposite semicircles ; 
for instance, if it is westerly on north it will be easterly on south. 

SEMIDIAMETER.— Half a diameter. The semidiameters 
of the sun and moon are given in the Nautical Almanac for every 
day of the year, but for purposes of practical navigation these 
may be called 16'. (See Corrected Altitude.) 

SEND OF THE SEA — (See Heave of the Sea.) 

SENSIBLE HORIZON.— A plane which is tangent to the 
surface of the earth where the observer is situated. This plane 
extends north, south, east, and west until bounded by the sky. 
(See Visible Horizon.) 

SET.— A heavenly body sets when its upper limb dips below 



128 THE navigator's pocket-book 

the horizon line , an altitude is set when the sliding limb of the 
sextant is clamped against the arc ; the space (span) contained 
between the points of the dividers in measuring a distance on 
the chart is known as a set ; to set the ship's course is to com- 
mence steering in the calculated direction ; the set of a current 
is the direction of its flow. 

SEXTANT.— An instrument of reflection used by navigators 
for measuring the altitudes of heavenly bodies, and for observ- 
ing angles. It is of more delicate mechanism than the quadrant 
or octant, and where the former is graduated (or cut, as it is 
often called) to minutes, and the latter to 15" of arc, the sextant 
reads to 10". The engraving in the front of the book represents 
the navigator's sextant. 

Names of Various Parts. — A, the graduated arc ; the divi- 
sions of the arc are 10' each, and these are subdivided by the 
vernier to 10" ; H, the handle, by which the sextant is held in 
the right hand ; M, the mirror, or index-glass, at the end of the 
sliding limb ; m, the horizon-glass ; E, the magnifying telescope, 
for giving greater distinctness to the images, is placed in the 
line of sight and supported in the ring or collar, K, which can 
be moved by a screw at the back in a direction at right angles to 
the plane of the sextant, so that the axis of the telescope may be 
directed either toward the silvered or transparent part of the 
horizon-glass ; the vernier is read by means of the magnifying- 
glass, R, attached to a revolving arm, S, which is secured upon 
the index bar or sliding limb ; P and Q, the colored shade- 
glasses, for shielding the e} 7 e from the glare of the sun ; P, the 
shades through which the image of the sun passes from the mir- 
ror to the horizon-glass ; Q, the back shade-glasses for protect- 
ing the eye from the glare of the horizon showing through the 
unsilvered part of the horizon-glass ; B, the tangent screw (set 



THE KAVIGATOll's POCKET-BOOK 129 

tangent to the plane of the instrument) by which the vernier may 
be moved delicately along the arc after the sliding limb has been 
clamped by the screw C at the back ; I, the inverting telescope ; 
F, the simple tube without glasses for giving a direct line of 
sight from the centre of the telescope ring to the horizon-glass. 

The inverting telescope, with its parallel wires, is principally 
used for measuring angular distances of heavenly bodies — a 
branch of nautical astronomy that does not come within the 
limits of this work. Altitudes may be measured by it in place 
of either of the other telescopes, but it requires considerable 
practice and a very steady hand. As its name implies, objects 
viewed through it appear upside down, so that to measure an 
altitude by it the navigator would bring the horizon down to the 
sun, instead of the sun down to the horizon. 

The small key shown is for adjusting the horizon-glass, and 
the small ring beside it contains a colored glass, and this may be 
screwed on the eye end of the telescopes as a substitute for the 
shacle-glasses. 

The star telescope contributes illuminating power to an obser- 
vation owing to its short tube and large object-glass, and permits 
the navigator to see the horizon distinctly when otherwise it 
would be obscured. If not provided with this valuable adjunct 
the navigator should have one fitted to his sextant, and be partic- 
ular that its collimation adjustment is made perfect. 

Adjustment of the Index-Glass. — This glass must be per- 
pendicular to the plane of the sextant. To. prove this, set the 
vernier to about the centre of the arc and clamp it, then look 
obliquely into the index-glass and observe if the arc seen direct 
and its reflection form one continuous line ; if so, the glass is 
perpendicular to the plane of the instrument, but if the reflected 
image appears to be lower than the other it proves that the glass 
9 



130 THE NAYIGATOK'S POCKET-BOOK 

leans backward ; if, however, the reflected image appears to be 
higher than the other the glass leans forward. 

Adjustment of the Horizon-Glass. — This glass must also be 
perpendicular to the plane of the sextant. To test this, let zero 
on the vernier cut zero on the arc, and hold the instrument al- 
most horizontal, noting if the direct and reflected images of the 
horizon line coincide — that is, if they show as an unbroken line 
both in the silvered and clear parts of the glass. If they do, the 
horizon-glass is perpendicular, but if they do not, then adjust 
the glass to the required angle by the adjusting screw. 

The Two Glasses to Be Parallel.— With the two zeros cut- 
ting, hold the instrument vertically, and if the direct and 
reflected images of the horizon line show as an unbroken and 
continuous line the horizon-glass is parallel to the index-glass, 
but if they do not show in an unbroken line adjust the horizon- 
glass by its adjusting screw. 

To Find the Index Error. — Should it prove impossible to 
obtain a perfect adjustment find the error of the instrument as 
follows : let the two zeros cut, then holding the instrument 
vertically look at the horizon and gently finger the tangent 
screw so as to move the vernier either forward or backward along 
the arc until the image of and the horizon line itself show in an 
unbroken line across the glass ; then the difference between zero 
on the vernier and zero on the arc will be the index error, and 
the amount of same will be added to any altitude observed by 
the instrument if zero on the vernier is to the right hand (off the 
arc) of zero on the arc, but the amount will be subtracted if 
zero on the vernier is to the left hand (on the arc) of zero on 
the arc. 

Telescope Adjustment. — Screw T in the telescope containing 
the two parallel wires and see that they are turned until parallel 



THE NAVIGATOR'S POCKET-BOOK 131 

with the plane of the sextant ; then select two stars, at least 90° 
apart, and make an exact contact at the wire nearest the plane 
of the instrument, and read the measured angle. Move the 
sextant so as to throw the objects on the other wire, and if the 
contact is still perfect the axis of the telescope is in its right situ- 
ation and the telescope adjustment is correct. If the images 
have separated it shows that the object end of the telescope 
droops toward the plane of the sextant, and if the images over- 
lap it proves that the object end of the telescope points away 
from the plane of the instrument. This will be rectified by the 
screws in the collar of the sextant. A defect in the telescope 
adjustment always makes angles too great. (See Axis of Col- 
limation.) 

Tormenting a Sextant. — The author desires to caution 
navigators against tormenting a sextant continually. A good 
instrument once placed in perfect adjustment (unless it meets 
with a heavy jar or fall) will keep in adjustment for a long time, 
and if let alone will give more satisfactory work than if the 
threads of the adjusting screws have become loose and worn 
from incessant slacking and setting up. 

To Read the Sextant Altitude. — Ascertain by looking toward 
the left how many degrees and ten-minute divisions the vernier 
zero has passed on the arc, then look along the vernier to the left 
until one of its lines coincides exactly with one of the lines of the 
arc, and the number of vernier minutes and ten-second divisions 
given will be added to the degrees and minutes originally ob- 
tained on the arc, and the sum of the two will be the altitude. 
To this altitude will be applied the index error (if any exists) in 
order to obtain the corrected observed angle. 

Remarks. — The quadrant, octant, and sextant are constructed 
on the same principle. Although the real arcs of these instru- 



132 the navigator's pocket-book 

ments are respectively only 45°, 60°, and 70°, yet owing to their 
double reflection they measure angles of 90°, 120°, and 140 c . 

SHADE-GLASSES.— (See Sextant.) 

SHADOW-PIN. — A straight, slender pin arranged to stand 
vertically on the centre of the glass of the compass bowl. It is 
portable and is set in place when required for the purpose of 
obtaining bearings of the sun. As its name indicates, it casts a 
shadow, and the opposite point of the compass from that on 
which the shadow falls is accepted as the bearing of the body. 
The shadow-pin may be employed for taking bearings generally, 
but it is not as satisfactory as an azimuth attachment or the 
pelorus. 

SHAPING THE COURSE.— (See Chart Sailing ; Great- 
Circle Sailing ; Mercator's Sailing ; Middle-Latitude Sailing.) 

SHIP TIME.— The hour shown by the ship's clock, which 
is set to apparent time or solar time. This may be done roughly 
by turning the hands of the clock to twelve (noon) when the sun 
crosses the meridian, or by allowing for the number of miles 
sailed east or west since the clock was last set. To accomplish 
this simply add to the face of the clock four minutes of time for 
every degree sailed east and subtract four minutes for every de- 
gree sailed west since the clock w r as last set on solar time. The 
most correct way is to proceed according to the rule given under 
the head of Regulating. 

SHORE RATE.— (See Rate.) 

SIDEREAL.— Relating to the stars. 

SIDEREAL DAY. — The interval between two successive 
transits of the same star over the same meridian ; the period of 
time in which the earth performs a complete revolution on its 



THE NAVIGATOR'S POCKET-BOOK 133 

axis. The length of a sidereal day is 23 h. 56 m. 04 sec., so that 
a sidereal day is shorter than a mean solar day by 3 m. 56 sec. 

SIDEREAL NOON.— This occurs when the First Point of 
Aries comes to the meridian. 

SIDEREAL TIME.— Time measured by the stars. Sidereal 
time commences when the .First Point of Aries is on the me- 
ridian and is counted from one hour to twenty-four hours, when 
the same point returns to the meridian again. 

SIGHT. — To take a sight is to measure the altitude of a 
heavenly body. 

SLIDING LIMB.— (See Sextant.) 

SLIP OF WHEEL.— The difference between the speed 
shown by a steam vessel and the speed that would be attained 
provided the propeller or paddle-wheels acted upon a solid sub- 
stance in place of a fluid. Slip of wheel is often referred to as 
the lost motion of the propeller. It is customary to allow a cer- 
tain number of revolutions to the mile, and according to this the 
estimated distance run by the vessel is compared with the actual 
distance run by observation, and the difference, expressed as a 
per centum, is entered in the log-book under the head of slip of 
wheel. Head winds and seas often retard a vessel's speed so that 
the slip of wheel reaches 50 per cent, and more. 

SOLAR.— Relating to the sun. 

SOLAR DAY. — The time which elapses between two succes- 
sive transits of the sun over the same meridian. 

SOLAR SYSTEM.— The sun and the heavenly bodies revolv- 
ing around it ; namely : Mercury, Venus, Earth, Moon, Mars, 
Jupiter, Saturn, Uranus, and Neptune. 

SOLAR TIME.— Time measured by the sun. When the sun 



134 the navigator's pocket-book 

crosses the meridian of the observer it is apparent noon at his 
place. 

SOLSTICES.— Those times of the year when the sun is at its 
greatest distance from the equator ; when its declination is 23£° 
north or 23^° south. 

SPECULUM. — A mirror ; the reflecting glass on an azimuth 
attachment. 

SPHERE. — According to geography, a representation of the 
earth's surface, and according to astronomy, the celestial con- 
cave. 

SPHERICAL.— Globular. 

SPHERICAL SAILINGS.— Great-Circle, Mercator, Middle- 
Latitude and Parallel Sailings. 

SPHERICAL TRIANGLE.— A portion of the surface of a 
sphere, contained by the arcs of three great circles. 

SPHERICAL TRIGONOMETRY.— That branch of trig- 
onometry which deals with the method of solving spherical 
triangles. 

SPIRIT COMPASS.— A liquid compass. 

SPRING EQUINOX. — When the sun crosses the equator 
from southern into northern declinations. This is known as the 
First Point of Aries. The Spring Equinox is often referred to as 
the Vernal Equinox. (See First Point of Aries.) 

STANDARD COMPASS. — One of the ship's compasses 
placed where it is least influenced by deviation, and by which 
the vessel is navigated. 

STANDARD TIME. — Time shown by a watch or clock set 
to mean solar time. (See Mean Sun.) 



THE NAVIGATOR'S POCKET-BOOK 135 

STARS.— (See Fixed Stars.) 

STAR TELESCOPE.— (See Sextant.) 

STAR TIME.— Same as sidereal time. 

STATION POINTER.— An instrument made use of in ma- 
rine surveying. It consists of a circle of brass graduated in de- 
grees, and is provided with, one fixed and two movable arms 
which project from its centre, so that the former may be set to 
any required angle. It is used sometimes on board ship when 
sailing along the coast, so as to locate the vessel's position by 
observing bearings of objects on shore. (See Telemeter.) 

STATUTE MILE.— (See Mile.) 

STEERING COMPASS.— That particular compass referred 
to by the wheelsman in steering the ship. The vessel is placed 
on her course by the standard compass, then whatever point is 
indicated at the time by the steering compass shows the course 
for the wheelsman to keep the vessel on according to that com- 
pass. 

STELLAR.— Relating to the stars. 

SUB-PERMANENT MAGNETISM.— After a new iron 
ship has been launched, it has been found that the magnetism 
induced in the hull while building rapidly diminishes, but by 
no means departs entirely, and that which remains is called sub- 
permanent magnetism. 

SUMNER'S METHOD.— A process employed for finding 
by a chronometer observation of the sun, or other heavenly 
body, the true latitude and longitude of the ship, especially when 
the latitude by dead reckoning cannot be relied upon. This is 
one of the most valuable problems within the sphere of the 
navigator, and should be practised by him until proficiency is 



13G the navigator's pocket-cook 

attained. In reality it consists of simply working out the lon- 
gitude several times by either the sun or the moon, a planet or 
fixed star. In the following we will consider that the sun is 
employed, consequently the longitudes will be ascertained 
according to the rule given under the head of "Longitude by 
One Altitude of the Sun." In case this problem is worked by 
the moon or by a planet or a star, then the longitudes will be 
found according to the respective rules given for those bodies 
under the head of Longitude ; but the lines on the chart will be 
drawn and the position of the vessel plotted in precisely the 
same way as described below for the sun. This problem in 
character is similar to and its result the same as that derived 
from what is known as the Combined Altitude Problem, or the 
Double Altitude Problem, but it employs fewer figures and as a 
natural consequence is simple in comparison and more easily 
worked than the other. 

Rule. — Assume two latitudes, one 80' (miles) less, and the 
other 30' greater than the latitude by dead reckoning, then ob- 
serve a regular time sight of the sun and work it up as usual, 
employing either of the assumed latitudes, and mark the result 
on the chart. Now work the same sight over again, using the 
other assumed latitude. Mark this answer also on the chart and 
draw a pencil line from one dot to the other. This is known as 
a line of bearing, and the ship will be somewhere on this line. 

The next thing required is to locate the vessel on this line of 
bearing. To effect this wait until the sun has changed ils 
azimuth (bearing) at least 2-J points (four or more would be 
better) then observe another regular time sight and work it up 
twice as before, making use of the same two assumed latitudes. 
Mark these two results on the chart and connect them also with 
a pencil line, which call the second line of bearing. It will be 



POCKET-BOOK 137 

seen that the first and second pencil lines cross one another. 
Now this intersection points out the ship's place provided she 
has remained stationary between observations, but if not, then 
the course and distance sailed after the first observation was 
taken must be considered as follows : 

Lay off (in pencil) from any part of the first line of bearing 
the true course and distance sailed in the interval between 
sights, and through the termination of this course and distance 
draw a line parallel to the first line of bearing, and where this 
last line drawn intersects the second line of bearing will be the 
ship's place. 

Remarks. — Instead of using assumed latitudes 30' different 
from the latitude by account, the navigator may extend this 
amount to 1° if he so prefers. 

When the first line is drawn on the chart for the purpose of 
connecting the first two pencil dots, the navigator knows that 
lie is somewhere on this line, and provided the line is not paral- 
lel to the coast, its extension will run into the land, so that if 
the ship is headed to sail on this line of bearing toward the 
coast, she will ultimately reach the point into which the line 
runs. The same applies as well to the second line of bearing. 

It has already been explained that when the second line of 
bearing has been drawn on the chart, the ship's place is fixed. 

This problem has been styled by some navigators as an astro- 
nomical cross-bearing. 

SUN. — The centre of the solar system : diameter, 885,000 
miles ; mean distance from the earth, 95,000,000 miles ; mean 
apparent diameter, 32' ; circumference, 2,780,000 miles. 

SUN DOG. — A luminous spot occasionally seen in the heavens 
near the sun. 



138 

SUNRISE AND SUNSET SIGHTS.— (See Longitude.) 

SUN TIME. — Same as solar time. 

SWINGING SHIP. — When the vessel is turned in a circle 
so that her head is brought consecutively to the thirty-two 
points of the compass, the operation is known as swinging ship. 
This is performed in compass-adjusting, the purpose being to 
note, while on each point, the compass-bearing of some distant 
but well-defined object, the correct magnetic bearing of which 
is known. 

SYMBOLS.— (See Log Book.) 

TAFFRAIL LOG. — A patent log, the register of which se- 
cures to the taffrail. (See Patent Log.) 

TAKING DEPARTURE.— (See Departure.) 

TANGENT SCREW.— (See Sextant.) 

TELEMETER. — An instrument consisting of two parallel 
base bars, divided by scales to tenths of an inch and ranging from 
to 20 inches on each bar. The object of this instrument is to 
mechanically solve problems that involve the parts of a plane 
triangle. It is only of use when sailing along the coast, when 
it affords a ready means of locating the ship by observing shore 
bearings, such as light-houses, prominent headlands, etc. 

TELL-TALE. — An inverted compass suspended from over- 
head in the cabin, or elsewhere below, 

TERRESTRIAL.— Relating to the earth. 

TERTIARY-MERIDIANS.— Those connected with second- 
ary meridians by carrying time in the most careful manner. (See 
Secondary Meridians.) 

THERMOMETER. — An instrument used for measuring 



THE NAVIGATOR'S POCKET-BOOK 139 

the variations of temperature. Fahrenheit's thermometer is a 
mercurial column so graduated as to have 180° between the 
freezing and boiling points of water. The freezing point of 
water on this thermometer is 32°, and the boiling point 212°. 
To indicate degrees below zero, it is common to preface them 
with the minus ( — ) sign. A Centigrade thermometer is a mer- 
curial column so graduated as to have 100 c between the freezing 
and boiling points of water, zero being the freezing point. 

To reduce Centigrade reading to Fahrenheit, multiply by 9, 
divide by 5 and add 32. 

To reduce Fahrenheit to Centigrade, subtract 32, multiply by 
5 and divide by 9. 

TIME.— (See Apparent, Astronomical, Civil, Greenwich, 
Local- Apparent, Mean, Mean-Solar, Ship, Sidereal, Solar, Stand- 
ard, Star, and Sun Times. See also Equation of Time.) 

TIME COURSE —During fog, while navigating in waters 
where it is necessary to change the course at certain fixed points 
in order to keep in the channel, or to avoid danger, the employ- 
ment of time courses becomes imperative. In order to run these, 
the course and distance from point to point is measured on the 
chart, and the speed of the vessel taken into account. As soon 
as the calculated period of time has expired, it is considered that 
the required distance has been run, and the course is accord- 
ingly changed. 

If there is a current flowing with, or against, or across the 
ship's course, the same must be allowed for. 

When threading coral reefs that are submerged, time courses 
are often employed. 

TIME SIGHT. — An observation of a heavenly bocty taken 
for the purpose of ascertaining the longitude. (See Longitude.) 



140 THE XAVIGATOIi'S POCKET-BOOK 

TRANSIT. — The passage of a heavenly body across the 
meridian. (See Lower Transit ; Upper Transit,) 

TRAVERSE. — An irregular track made by a vessel on ac- 
count of having sailed several courses. 

TRAVERSE SAILING.— (See Traverse.) 

TRAVERSE TABLES.— Tables containing the difference 
of latitude and departure for quarter points and for single de- 
grees of the compass, calculated for intervals of one mile and 
extending to three hundred miles. By these tables the solution 
of right-angle triangles is accomplished by mere inspection. The 
form that a navigator rules for working out his dead reckoning 
is a traverse table for the particular courses sailed by his ves- 
sel. 

TRIGONOMETRY.— The science of measuring triangles. 

TRIPOD COMPASS. — A compass elevated on a three-leg 
stand, on the principle of the pole compass. 

TROPIC OF CANCER.— The parallel of 23° 28' north— 
the highest northern point of the sun's declination, which it 
reaches on June 21st. 

TROPIC OF CAFRICORN.—The parallel of 23° 28' south. 
— the highest southern point of the sun's declination, which it 
reaches on December 21st. 

TRUE-CENTRAL-ALTITUDE. — (See Corrected Alti- 
tude.) 

TYPHOON.— (See Law of Storms.) 

UPPER LIMB. — The highest part of the circumference of 
the sun and moon ; the part situated directly above the centre- 
When the image of the lower portion of the disk of the sun or 
moon is brought in contact with the horizon, it is 'said that the 



THE KAVIGATOR'S POCKET-BOOK 141 

altitude of the lower limb is observed, and when the image of 
the upper portion of the disk is brought in contact with the hori- 
zon, it is said that the altitude of the upper limb is observed. 
(See Corrected Altitude.) 

UPPER TRANSIT.— The passage of a heavenly body over 
the meridian when the body is moving from east to west. The 
Nautical Almanac gives the astronomical times of the upper 
transits of heavenly bodies. The body having risen until it 
crossed the meridian above the pole, while moving from east to 
west, it declines to the west, then curves eastward, continuing 
to fall until it crosses the meridian below the pole— 180° distant 
from the meridian of its upper transit. It then commences to 
rise, still moving eastward, and when midway between the 
meridians'of its upper and lower transits, it curves westward 
and continues to rise until it again makes its upper transit. (See 
Lower Transit.) 

VARIATION. — The divergence of the compass needle from 
the true north of the heavens. This is not constant. In the 
year 1663 in Paris, the needle pointed true north, previous to 
which the variation had been easterly. From the year 1663 to 
the year 1814, the westerly variation in Paris steadily increased, 
until in the latter year it amounted to 22^°. From the year 1814 
it has steadily decreased, but is still westerly. (See Compass ; 
Amplitude ; Azimuth.) 

VARIATION CHART.— (See Chart.) 

VERNAL EQUINOX.— (See Spring Equinox.) 

VERNIER. — The graduated scale on the sliding limb or in- 
dex bar of the sextant. (See Sextant.) 

VERTEX. — That point of the heavens situated perpendicu- 



142 the navigator's pocket-book 

larly above the observer's head ; the angular point, or the point 
where the two legs or sides of an angle meet. 

VERTICAL. — Perpendicular to the horizon. 

VERTICAL CIRCLE.— A great circle of the sphere which 
passes through the zenith and nadir of a place. 

VERTICAL DANGER ANGLE.— (See Danger Angle.) 

VISIBLE HORIZON.— The boundary or limit of the obser- 
ver's view is termed the visible or apparent horizon. The angle 
between the sensible and visible horizons is known as the dip of 
the horizon. 

WATCHES.— (See Log-Book.) 

WEATHER. — The signs or indications by which the coming 
weather may be anticipated are as follows : 

A rosy sky at sunset, fine weather ; a bright yellow sky at 
sunset, wind ; a pale yellow sky at sunset, wet ; orange or cop- 
per colored sky, wind and rain ; sickly greenish hue, wind and 
rain ; tawny or coppery clouds, wind ; a dark red sky, rain ; 
a red sky in the morning, bad weather ; a gray sky in the morn- 
ing, fine weather ; a high dawn, wind ; a low dawn, fair 
weather ; soft or delicate clouds, fine weather with light breezes ; 
hard-edged, oily looking clouds, wind ; a dark, gloomy, blue 
sky, wind ; light, bright-blue sky, fine weather ; light, delicate 
tints with soft, indefinite forms of cloud, fine weather ; gaudy 
or unusual hues with hard, definitely outlined clouds, rain and 
wind ; small, inky clouds, rain ; high upper clouds crossing the 
heavens in a direction different from that of the lower clouds, or 
of the wind felt below, foretell a change of wind in the direc- 
tion of the upper clouds ; when sea birds fly out far to seaward, 
moderate wind and fair weather may be expected ; when sea 



THE NAVIGATOR'S POCKET-BOOK 143 

birds bang about the land or fly inland, strong winds and stormy- 
weather are promised ; dew is an indication of coming fine 
weather. 

Cirrus. — Also known as the mare-tail cloud, composed of 
streaks, wisps, and fibres ; a cloud of the least density and 
greatest elevation, showing the widest range of direction and 
variety of form. Settled weather is to be expected when groups 
of cirri are to be seen during a gentle wind after severe weather 
has been experienced. When streaks of cirri extend across the 
sky conforming to the direction in which a light wind is blow- 
ing, the wind will remain steady but increase. When fine 
threads of cirri are blown or brushed backward at one end, the 
surface wind will veer around to that point. 

Cumulus. — This is also known as the day cloud and the sum- 
mer cloud. It forms only in the day-time during the summer, 
and results from the rise of vapors from rivers, lakes, etc., into 
the colder atmosphere. Fine, calm, and warm weather may be 
anticipated when cumuli take on a moderate size and delicate 
color ; but cold, rainy, and heavy weather may be expected 
when cumuli in dense, dark masses roll acress the sky, sink low- 
er, and do not disappear at sunset. 

Stratus. — Also called the night cloud. It hangs the lowest of 
the various clouds, obtains its greatest density about midnight, 
and disappears when the sun rises. It is formed by the conden- 
sation of vapors from lakes, marshes, etc., appearing as an ex- 
tended sheet of white mist near to the earth, and sometimes 
touching it. 

Cirro-Cumulus. — This is known as well by the name of a 
mackerel sky. It is seen in small, rounded masses, looking like 
flocks of sheep lying down, and in consequence is referred to at 
times as sheep in-a -meadow sky. It is principally seen in summer, 



114 THE NAVIGATORS POCKET-BOOK 

and indicates warm, dry, weather. When cirro-cumulus occurs 
in winter, a thaw and wet weather may be expected. 

Cirro-Stratus. — Also referred to as the vane cloud, the slioal 
of -fish cloud, and the mackerel-backed cloud. A storm of rain or 
snow may be expected when this cloud is seen. As it name sig- 
nifies, this cloud exhibits a mingling of the characteristics of 
the cirrus and stratus, being dense in the middle and tapering 
toward the edges. 

Oumulo-Stratus. — A blending or mingling of the cumulus 
and cirro-stratus, appearing at times as a thick bank of cloud 
with overhanging edges. What is known as a distinct-cumulo- 
stratus cloud appears as a cumulus cloud surrounded on all sides 
by small fleecy clouds. When cumulo-stratus clouds are seen 
sudden atmospheric changes may be expected. 

Nimbus, or Cumulo-Cirro- Stratus. — Called the rain cloud. 
As it name signifies, it is a combination of the three primary 
forms of cloud. The cirro-stratus overspreads the sl^y, and un- 
derneath it the cumulus clouds drive in from windward until 
they form one continuous mass, settling down in a horizontal 
sheet from which rain falls. 

Cloud Scale. — The amount of cloud is denoted by a numer- 
ical scale of to 10 — indicating a clear sky, 5 a sky half cov- 
ered, and 10 a totally obscured sky. 

Rainbows. — When rainbows are observed in the morning 
they promise wet weather, but when observed in the evening 
they promise clear weather. 

WIND. — The wind, as a rule, shifts with the sun ; but 
whereas this means from left to right (or with the hands of a 
clock) in the northern hemisphere, it means from right to left 
(or against the hands of a clock) in the southern hemisphere. 
This is known as veering. When the wind shifts in the contrary 



THE KAVIGATOir'S POCKET-BOOK 145 

direction it is known as backing. There is an old sea couplet 
which applies with truthfulness to the shifting of the wind : 

' ' When the wind shifts against the sun, 
Trust it not, for back it will run." 

In the northern hemisphere the veering, or proper shifting of 
the wind would be from east to west by the way of south-east, 
south, and south-west, and the backing of the wind would be 
from east to west by the way of north-east, north, and north- 
west. 

In the southern hemisphere the above rule would be reversed. 

When the wind backs it may be accepted as a sign that the 
weather is unsettled, and that the wind will come out again from 
its original quarter. 

Winds are named from the direction in which they blow, 
hence a north wind comes out of the north. 

ZENITH. — That point in the heavens vertically overhead of 
the observer, and 90° distant from every point of the horizon. 
Opposed to nadir. (See Nadir.) 

ZENITH DISTANCE.— What an altitude lacks of 90°, or 
the complement of an altitude ; the angular distance of a heav- 
enly body from the zenith of the observer. 

ZERO. — The point at which the cutting or graduation of a 
sextant, etc., commences. 

ZODIAC — An imaginary zone in the celestial concave in 
which the sun, moon, and larger planets appear to perform their 
revolutions. 

ZONE. — There are five zones : the torrid zone extending 
10 



146 the navigator's pocket-book 

from the equator to 23° 28' north and south ; the temperate 
zones extending from 23° 28' north and south to 66° 32' north 
and south, and the frigid zones extending from 66° 32' north 
and south to the poles. 



TABLES 






THE E"AYIGATOR S POCKET-BOOK 



149 







TABLE OF CORRECTION 














TO BE APPLIED 


TO THE 










TRUE ALTITUDE OF THE POLAR STAR. 






R. A. 

Merid- 


1 
Cor- 
rection. J 


R. A. 

Merid- 


Cor- 
rection. 


R. A. 

Merid- 


Cor- 
rection. 


R. A. 

Merid- 


Cor- 
rection. 


ian. 




ian. 




ian. 




ian. 




h. m. 


o / 


h. 


m. 


o / 


h. 


m. 


o / 


h. 


m. 


o / 





-1 10 


6 


00 


— 20 


12 


00 


+ 1 10 


IS 


00 


+ 26 


10 


-^1 12 


6 


10 


— 23 


12 


10 


+ 1 12 


IS 


10 


+ 23 


20 


— 1 12 


6 


20 


— 19 


12 


20 


+ 1 12 


18 


20 


+ 19 


30 


— 1 13 i 


G 


30 


— 10 


12 


30 


+ 1 13 


18 


30 


+ 16 


40 


— 1 14 | 





40 


— 13 


12 


40 


+ 1 14 


IS 


40 


+ 13 


50 


— 1 14 


(5 


50 


— 10 


12 


50 


+ 1 14 


18 


50 


+ 10 


1 00 


— 1 15 \ 


7 


00 


— 7 


13 


00 


+ 1 15 


19 


00 


+ 7 


1 10 


— 1 15 


7 


10 


— 3 


13 


10 


+ 1 15 


19 


10 


+ 3 


1 20 


— 1 15 


7 


20 





13 


20 


+ 1 15 


19 


20 





1 30 


-1 15 


7 


30 


+ 03 


13 


30 


+ 1 15 


19 


30 


— 3 


1 40 


-1 15 


7 


40 


+ 7 


13 


40 


+ 1 15 


19 


40 


— 7 


1 50 


^-1 14 


7 


50 


+ 10 


13 


50 


+ 1 14 


19 


50 


— 10 


2 00 


— 1 14 


8 


00 


+ 13 


14 


00 


+ 1 14 


20 


00 


— 13 


2 10 


— 1 13 


8 


10 


+ 10 


14 


10 


+ 1 13 


20 


10 


— 16 


2 20 


— 1 12 


8 


2.) 


* 19 


14 


20 


+ 1 12 


20 


20 


— 19 


2 30 


— 1 11 


8 


30 


+ 23 


14 


30 


+ 1 12 


20 


30 


— 23 


2 40 


— 1 10 


8 


40 


+ 26 


14 


40 


+ 1 10 


20 


40 


— 26 


2 50 


-1 9 


8 


50 


+ 29 


14 


50 


+ 1 9 


20 


50 


— 29 


3 00 


— 1 8 


9 


00 


+ 32 , 


15 


00 


+ 18 


21 


00 


— 32 


3 10 


— 1 T 


9 


10 


+ 35 ! 


15 


10 


+ 1 7 


21 


10 


— 35 


3 20 


— 1 5 


9 


20 


+ 37 


15 


20 


+ 15 


21 


20 


-0 37 


3 30 


— 1 3 


9 


30 


+ 40 


15 


30 


+ 13 


21 


30 


— 40 


3 40 


-1 1 


9 


40 


+ 43 


15 


40 


+ 11 


21 


40 


— 43 


3 50 


— 59 


9 


50 


+ 46 


15 


50 


+ 59 


21 


50 


— 46 


4 00 


— 57 


10 


00 


+ 48 


16 


00 


+ 57 


22 


00 


-0 48 


4 10 


— 55 


1 10 


10 


+ 51 


16 


10 


+ 55 


22 


10 


— 51 


4 20 


— 53 


10 


20 


+ 53 


16 


20 


+ 53 


22 


20 


— 53 


4 30 


— 51 


10 


30 


+ 55 


16 


30 


+ 51 


22 


30 


— 55 


4 40 


— 4S 


10 


40 


+ 57 


16 


40 


+ 48 


22 


40 


— 57 


4 50 


— 4(5 


10 


50 


+ 59 


16 


50 


+ 46 


22 


50 


— 59 


5 00 


— 43 


11 


00 


+ 11 


17 


00 


+ 43 


23 


00 


— 1 1 


5 10 


— 40 


11 


10 


+ 13 


17 


10 


+ 40 


23 


10 


— 1 3 


5 20 


— 37 


11 


20 


+ 15 


17 


20 


+ 37 


23 


20 


— 15 


5 30 


— 35 


11 


30 


+ 17 


17 


30 


+ 35 


23 


30 


— 1 7 


5 40 


— 32 


11 


40 


+ 1 8 


17 


40 


+ 32 


23 


40 


— 1 8 


5 50 


— 29 


11 


50 


+ 19 


17 


50 


+ 29 


23 


50 


— 1 9 


6 00 


— 26 


12 


00 


+ 1 10 


18 


00 


+ 26 


24 


00 


— 1 10 



150 



THE NAVIGATOR S POCKET-BOOK 



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Astronomical Apparent Time of Crossing the Meridian of the Ship. 


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3 14 

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15 02 

12 37 

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14 08 
23 51 

6 20 

13 50 
9 02 

21 24 

22 00 
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6 02 4 05 
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1 40,23 43 

15 59 14 02 
21 32 10 35 

7 15 5 18 

17 18 15 21 
10 03 17 06 

16 38 14 41 

49 22 52 
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3 52 1 55 
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17 51 15 54 
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THE XAVIGATOR S POCKET-BOOK 



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152 



THE NAVIGATOR S POCKET-BOOK 



TABLE OF DISTANCES 

At which Objects can be Seen at Sea, according to 
their respective elevations and the height op the 
Observer's Eye Above Sea-Level. 



Height 


Distance 


Height 


Distance 


Height 


Distance 


Height 


Distance 


in 


in Nauti- 


in 


in Nauti- 


in 


in Nauti- 


in 


in Nauti- 


Feet. 


cal Miles. 


Feet. 


cal Miles. 


Feet. 


cal Miles. 


Feet. 


cal Miles. 


5 


2.565 


55 


8.509 


110 


12.030 


450 


24.380 


10 


3.628 


60 


8.886 


120 


12.560 


500 


25.650 


15 


4.443 


65 


9.249 


130 


13.080 


550 


26.900 


20 


5.130 


70 


9.598 


140 


13.570 


600 


28.100 


25 


5 736 


75 


9.935 


150 


14.050 


650 


29.250 


80 


6.283 


80 


10.260 


200 


16.220 


700 


30.280 


35 


6.7S7 


85 


10.570 


250 


18.140 


800 


32.450 


40 


7.255 


90 


10.880 


300 


19.870 


900 


34.540 


45 


7.696 


95 


11.180 


350 


21 460 


1,000 


36.280 


50 


8.112 


100 


11 470 


400 


22.940 


* 


* 



Rule. — Add together the figures given for the height of eye 
above the sea-level and the figures given for the elevation of the 
object, and the answer will be the distance of the vessel from 
the object in question. 

"When a low-lying island, or shore, or the hull of a low-sided 
vessel is seen awash with the horizon, the distance of the hori- 
zon for the height of the observer's eye above the sea-level will 
alone give the distance from the object. 

Example.— The top of a lighthouse 150 feet high is seen 
awash when the observer's eye is 15 feet above the sea-level — 
required the distance of the observer from the light ? 

Height of eye, 15 feet = 4,443 miles. 
Height of light, 150 feet = 14,050 miles. 

Distance of observer from light, 18,493 = 18-J miles nearly. 



THE NAVIGATOR S POCKET-BOOK 



153 



PATTERSON'S DANGER-ANGLE TABLES. 




Heig 


lit of Light Above Sea-Level. 


Distance in 










1 ards. 












30 Feet. 


35 Feet. 


40 Feet. 


45 Feet. 




o / // 


o / // 


o / // 


O f ff 


100 


5 42 40 


6 39 20 


7 35 40 


8 31 50 


150.. 


3 48 50 


4 26 50 


5 04 50 


5 42 40 


200 


2 51 40 


3 20 20 


3 48 50 


4 17 20 


250 


2 17 30 


2 40 20 


3 03 10 


3 26 00 


300 


1 54 30 


2 13 40 


2 32 40 


2 51 40 


350 


1 38 10 


1 54 30 


2 10 50 


2 17 10 


400 


1 26 00 


1 40 10 


1 54 30 


2 08 50 


450." 


1 16 20 


1 29 10 


1 41 50 


1 54 30 


500 (im.). 


1 08 40 


1 20 10 


1 31 40 


1 43 10 


550 


1 02 30 


1 12 50 


1 23 20 


1 33 40 


600 


57 20 


1 06 50 


1 16 20 


1 26 00 


650 


52 50 


1 01 40 


1 10 30 


1 19 20 


700 


49 10 


57 20 


1 05 30 


1 13 40 


750 


45 50 


53 30 


1 01 10 


1 08 40 


800 


43 00 


50 10 


57 20 


1 04 30 


850. 


40 30 


47 10 


53 50 


1 00 40 


yoo 


38 10 


44 30 


51 00 


57 20 


950 


36 10 


42 10 


48 10 


54 20 


1000 (|m.) 


34 20 


40 10 


45 50 


51 30 



154 



THE NAVIGATORS POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 




Heig 


lit of Light Above Sea-Level. 


Distance in 










1 aids. 












30 Feet. 


35 Feet. 


40 Feet. 


45 Feet. 




o r // 


O 1 II 


o / // 


O 1 II 


1050 


32 40 


38 10 


43 40 


49 10 


1100 


31 10 


36 30 


41 40 


46 50 


1150 


29 50 


34 50 


39 50 


44 50 


1200 


28 40 


33 20 


38 10 


43 00 


1250 


27 30 


32 00 


36 40 


41 10 


1300 


26 30 


30 50 


35 20 


39 40 


1350 


25 30 


29 00 


34 00 


38 10 


1400 


24 30 


28 40 


32 40 


36 50 


1450 


23 40 


Q 27 40 


31 40 


35 30 


1500 (fm.) 


22 50 


26 40 


30 30 


34 20 


1550 


22 10 


25 50 


29 30 


33 20 


1600 


21 30 


25 00 


28 40 


32 10 


1650 


20 50 


24 20 


27 50 


31 10 


1700 


20 10 


23 30 


27 00 


30 20 


1750 


19 40 


22 50 


26 10 


29 30 


1800 


19 10 


22 20 


25 30 


28 40 


1850 


18 30 


21 40 


24 50 


27 50 


1900 


18 10 


21 10 


24 10 


27 10 


1950 


17 40 


20 30 


23 30 


26 30 


2000 (lm.) 


17 10 


20 00 


22 50 


25 50 



THE NAVIGATOR S POCKET-BOOK 



155 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Height of Light Above Sea Level. 


Miles 








and Tenths. 












50 Feet. 


55 Feet. 


60 Feet. 


65 Feet. 




O 1 II 


o / // 


o / // 


o / // 


0.1 


4 45 50 


5 14 10 


5 42 40 


6 11 00 


0.2 


2 23 10 


2 37 30 


2 51 40 


3 06 00 


0.3 


1 35 30 


1 45 00 


1 54 30 


2 04 00 


0.4 


1 11 40 


1 18 50 


1 26 00 


1 33 00 


0.5 


57 20 


1 03 00 


1 08 40 


1 14 30 


0.6 


47 40 


52 30 


57 20 


1 02 00 


0.7 


40 50 


45 00 


49 10 


53 10 


0.8. , 


35 50 


39 20 


43 00 


46 30 


0.9....... 


31 50 


35 00 


38 10 


41 20 


1.0 


28 40 


31 30 


34 20 


37 10 


1.1 


26 00 


28 40 


31 10 


34 00 


1.2 


24 00 


26 20 


28 40 


31 00 


1.3 


22 00 


24 10 


26 30 


28 40 


1.4 


20 30 


22 30 


24 30 


26 40 


1.5 


19 10 


21 00 


22 50 


24 50 


1.6.. 


17 50 


19 40 


21 30 


23 20 


1.7 


16 50 


18 30 


20 10 


21 50 


1.8 


15 50 


17 30 


19 10 


20 40 


1.9 


15 00 


16 30 


18 10 


19 40 


2.0....... 


14 20 


15 40 


17 10 


18 40 



156 



THE NAVIGATOR'S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


it of Light Ahove Sea-Level. 


Miles 










and Tenths. 












70 Feet, 


75 Feet. 


80 Feet. 


85 Feet. 




o / // 


o / // 


o / // 


o / // 


0.1 


6 39 20 


7 07 30 


7 35 40 


8 03 50 


0.2 


3 20 20 


3 34 30 


3 48 50 


4 03 10 


0.3 


2 13 40 


2 23 10 


2 32 40 


2 42 10 


0.4 


1 40 10 


1 47 20 


1 54 30 


2 01 40 


0.5 


1 20 10 


1 26 00 


1 31 40 


1 37 20 


0.6 


1 06 50 


1 11 40 


1 16 20 


1 21 10 


0.7 


57 20 


1 01 20 


1 05 30 


1 09 30 


0.8 


50 10 


53 40 


57 20 


1 00 50 


0.9 


44 30 


47 40 


51 00 


54 10 


1.0 


40 10 


43 00 


45 50 


48 40 


1.1 


36 30 


39 00 


41 40 


44 20 


1.2 


33 20 


35 50 


38 10 


40 30 


1.3 


30 50 


33 00 


35 10 


37 30 


1.4 


28 40 


30 40 


32 40 


34 50 


1.5 


26 40 


28 40 


30 30 


32 30 


1.6 


25 00 


26 50 


28 40 


30 30 


1.7 


23 40 


25 20 


28 00 


28 40 


1.8 


22 20 


23 50 


25 30 


27 00 


1.9 


21 10 


22 40 


24 10 


25 40 


2.0 


20 00 


21 30 


22 50 


24 20 



THE NAVIGATOR 3 POCKET-BOOK 



157 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Height of Light Above Sea-Level. 


Miles 
and Tenths. 


















70 Feet. 


75 Feet. 


80 Feet. 


85 Feet, 




O f ff 


o f ff 


o f ff 


o f ff 


2.1 


19 10 


20 30 


21 50 


23 10 


2.2 


18 10 


19 30 


20 50 


22 10 


2.3 


17 30 


18 40 


20 00 


21 10 


2.4....... 


16 40 


17 50 


19 10 


20 20 


2.5 


16 00 


17 10 


18 20 


19 30 


2.6 


15 20 


16 30 


17 40 


18 40 


2.7 


14 50 


15 50 


17 00 


18 00 


2.8 


14 20 


15 20 


16 20 


17 20 


2.9 


13 50 


14 50 


15 50 


■0 16 50 


3.0 


13 20 


14 20 


15 20 


16 10 


3.1 


13 00 


14 00 


14 50 


15 40 


3.2 


12 30 


13 30 


14 20 


15 10 


3.3 


12 10 


13 00 


13 50 


14 50 


3.4 


11 50 


12 40 


13 30 


14 20 


3.5 


11 30 


12 20 


13 10 


13 50 


3.6 


11 10 


0.12 00 


12 40 


13 20 


3.7 


10 50 


11 40 


12 20 


13 10 


3.8 


10 30 


11 20 


12 00 


12 50 


3.9 


10 20 


11 00 


11 40 


12 30 


4.0 


10 00 


10 40 


11 30 


12 10 



158 



THE NAVIGATOR S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


lit of Light . 


Above Sea-Level. 


Miles 










and Tenths. 












90 Feet. 


95 Feet. 


100 Feet. 


105 Feet. 




o / rt 


O f ft 


a i n 


o / // 


0.1 


8 31 50 


8 59 50 


9 27 40 


9 55 30 


0.2 


4 17 20 


4 31 30 


4 45 50 


5 00 00 


0.3 


2 51 40 


3 01 20 


3 10 50 


3 20 20 


0.4 


2 08 50 


2 25 00 


2 23 10 


2 30 20 


0.5 


1 43 10 


1 48 50 


1 54 30 


2 00 20 


0.6. 


1 26 00 


1 30 40 


1 35 30 


1 40 10 


0.7 


1 13 40 


1 17 40 


1 21 50 


1 26 00 


0.8 


1 04 30 


1 08 00 


1 11 40 


1 15 10 


0.9 


57 20 


1 00 30 


1 03 40 


1 06 50 


1.0 


51 30 


54 30 


57 20 


1 00 10 


1.1 


46 50 


49 30 


52 00 


54 40 


1.2 


43 00 


45 20 


47 40 


50 10 


1.3 


39 40 


41 50 


44 00 


46 20 


1.4 


36 50 


38 50 


40 50 


43 00 


1.5 


34 20 


36 20 


38 10 


40 10 


l.G 


32 10 


34 00 


35 50 


37 40 


1.7 


30 20 


32 00 


33 40 


35 20 


1.8 


28 40 


30 10 


31 50 


33 20 


1.9 


27 10 


28 40 


30 10 


31 40 


2.0 


25 50 


27 10 


28 40 


30 00 



THE NAVIGATOR'S POCKET-BOOK 



159 



PATTERSON'S DANGER- ANGLE TABLES. 


Distance in 


Heig 


bt of Liglit Above Sea-Level. 


Miles 










and Tenths. 


90 Feet. 


95 Feet. 


100 Feet. 


105 Feet. 




or?? 


Off/ 


o / // 


Q t ft 


2.1 


24 30 


25 50 


27 20 


28 40 


2.2 


23 30 


24 40 


26 00 


27 20 


2.3 


22 20 


23 40 


24 50 


26 10 


2.4 


21 30 


22 40 


23 50 


25 00 


2.5 


20 40 


21 50 


22 50 


24 00 


2.6 


19 50 


21 00 


22 00 


23 10 


2.7 


19 10 


20 10 


21 10 


22 20 


2.8 


18 20 


19 30 


20 30 


21 30 


2.9 


17 50 


18 50 


19 40 


20 40 


3.0. . ..... 


17 10 


18 10 


19 10 


20 00 


3.1 


16 40 


17 30 


18 30 


19 20 


3.2 


16 10 


17 00 


17 50 


18 50 


3.3 


15 40 


16 30 


17 20 


18 10 


3.4 


15 10 


16 00 


16 50 


17 40 


3.5 


14 40 


15 30 


16 20 


17 10 


3.6 


14 20 


15 10 


15 50 


16 40 


3.7 


14 00 


14 40 


15 30 


16 10 


3.8....... 


13 30 


14 20 


15 00 


15 50 


3.9 


13 10 
12 50 


14 00 
13 40 


14 40 

14 20 


15 20 
15 00 


4.0 



160 



THE NAVIGATOR'S POCKET-BOOK 



PATTERSON'S DANGER- ANGLE TABLES. 


Distance in 

Miles 
and Tenths. 


Height of Light Above Sea-Level. 


110 Feet. 


115 Feet. 


120 Feet. 


125 Feet. 


0.1 

0.2 

0.3 

0.4 

0.5 


O 1 II 

10 23 20 
5 14 10 
3 29 50 
2 37 30 

2 06 00 


Q 1 II 

10 51 00 
5 28 30 
3 39 20 
2 44 40 
2 11 40 


1 II 

11 18 40 
5 42 40 
3 48 50 
2 51 40 
2 17 30 


o / // 

11 46 10 
5 56 50 
3 58 20 

2 58 50 
2 23 10 


0.6 

0.7 

0.8 

9 


1 45 00 
1 30 00 
1 18 50 
1 10 00 
1 03 00 


1 49 50 
1 34 10 
1 22 20 
1 13 10 
1 05 50 


1 54 30 
1 38 10 
1 26 00 
1 16 20 

1 08 40 


1 59 20 
1 42 20 
1 29 30 
1 19 30 
1 11 40 


1.0. 


1.1 

1.2 

1.3 

1.4 

1.5 


57 20 
52 30 
48 30 
45 00 
42 00 


59 50 
54 50 
50 40 
47 00 
44 00 


1 02 30 

57 20 
52 50 
49 10 
45 50 


1 05 10 
59 40 
55 00 
51 10 

47 40 


1.6 

1.7 

1.8 

1.9 

2.0 


39 20 
37 00 
35 00 
33 10 
31 30 


41 10 
38 50 
36 40 
34 40 
33 00 


43 00 
40 30 
38 10 
36 10 
34 20 


44 50 
42 10 
39 50 
37 40 
35 50 



THE NAVIGATOR S POCKET-BOOK 



161 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heigl 


it of Light Above Sea-Level. 


Miles 










and Tenths. 












110 Feet. 


115 Feet. 


120 Feet. 


125 Feet. 




f ff 


o t ft 


O / ff 


Q t ft 


2.1 


30 00 


31 20 


32 40 


34 10 


2.2 


28 40 


30 00 


31 10 


32 30 


2.3 


27 20 


28 40 


29 50 


31 10 


2.4 


26 20 


27 30 


28 40 


29 50 


2.5 


25 10 


26 20 


27 30 


28 40 


2.6 


24 10 


25 20 


26 30 


27 30 


2.7 


23 20 


24 20 


25 30 


26 30 


2.8 


22 30 


23 30 


24 30 


25 30 


2.9 


21 40 


22 40 


23 40 


24 40 


3.0 


21 00 


22 00 


22 50 


23 50 


3.1 


20 20 


21 10 


22 10 


23 10 


3.2 


19 40 


20 30 


21 30 


22 20 


3.3 


19 10 


20 00 


20 50 


21 40 


3.4 


18 30 


19 20 


20 10 


21 00 


3.5 


18 00 


18 50 


19 40 


20 30 


3.6 


17 30 


18 20 


19 10 


19 50 


3.7 


17 00 


17 50 


18 30 


19 20 


3.8 


16 30 


17 20 


18 10 


18 50 


3.9 


16 10 


16 50 


17 40 


18 20 


4.0 


15 40 


16 30 


17 10 


17 50 



162 



THE NAVIGATOR'S POCKET-BOOK 



PATTERSON'S DANGER- ANGLE TABLES. 


Distance in 


Heig] 


it of Light . 


AJbove Sea-Level. 


Miles 










and Tenths. 












130 Feet. 


135 Feet. 


140 Feet. 


145 Feet. 




o i n 


Q 1 II 


O 1 II 


O 1 II 


0.1 


12 13 30 


12 40 50 


13 08 00 


13 35 10 


0.2 


6 11 00 


6 25 10 


6 39 20 


6 53 20 


0.3 


4 07 50 


4 17 20 


4 26 50 


4 36 20 


0.4 


3 06 00 


3 13 10 


3 20 20 


3 27 30 


0.5 


2 28 50 


2 34 40 


2 40 20 


2 46 00 


0.6 


2 04 00 


2 08 50 


2 13 40 


2 18 20 


0.7 


1 46 20 


1 50 30 


1 54 30 


1 58 40 


0.8 


1 33 00 


1 36 40 


1 40 10 


1 43 50 


0.9 


1 22 40 


1 26 00 


1 29 10 


1 32 20 


1.0 


1 14 30 


1 17 20 


1 20 10 


1 23 00 


1.1 


1 07 40 


1 10 20 


1 12 50 


1 15 30 


1.2 


1 02 00 


1 04 30 


1 06 50 


1 09 10 


1.3 


57 20 


59 30 


1 01 40 


1 03 50 


1.4 


53 10 


55 10 


57 20 


59 20 


1.5 


49 40 


51 30 


53 30 


55 20 


1.6 


46 30 


48 20 


50 10 


51 50 


1.7 


43 50 


45 30 


47 10 


48 50 


1.8 


41 20 


43 00 


44 30 


46 10 


1.9 


39 10 


40 40 


42 10 


43 40 


2.0 


37 10 


38 40 


40 10 


41 30 



THE NAVIGATOK S POCKET-BOOK 



163 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


it of Light Above Sea-Level. 


Miles 










and Tenths. 


130 Feet. 


135 Feet. 


140 Feet, 


145 Feet. 




o r ft 


O 9 ft 


O / ft 


Q t ft 


2.1 


35 30 


36 50 


38 10 


39 30 


2.2 


33 50 


35 10 


36 30 


37 50 


2.3 


32 20 


33 40 


34 50 


36 10 


2.4 


31 00 


32 10 


33 20 


34 40 


2.5 


29 50 


31 00 


32 00 


33 10 


2.6 


28 40 


29 40 


30 50 


32 00 


2.7 


27 30 


28 40 


29 40 


30 50 


2.8 


26 40 


27 40 


28 40 


29 40 


2.9 


25 40 


26 40 


27 40 


28 40 


3.0 


24 50 


25 50 


26 50 


27 40 


3.1 


24 00 


25 00 


25 50 


26 50 


3.2 


23 20 


24 10 


25 00 


26 00 


3.3 


22 30 


23 30 


24 20 


25 10 


3.4 


21 50 


22 40 


23 30 


24 30 


3.5 


21 20 


22 10 


22 50 


23 40 


3.6 


20 40 


21 30 


22 20 


23 00 


3.7 


20 10 


20 50 


21 40 


22 30 


3.8 


19 40 


20 20 


21 10 


21 50 


3.9 


19 10 


19 50 


20 30 


21 20 


4.0....... 


18 40 


19 20 


20 00 


20 50 



164 



THE NAVIGATORS POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


ht of Light Above Sea-Level. 


Miles 
and Tenths. 










150 Feet. 


155 Feet. 


160 Feet. 


165 Feet. 




O 1 II 


O t ft 


O 1 II 


O 1 II 


0.1 


14 02 10 


14 29 00 


14 55 50 


15 22 30 


0.2 


7 0? 30 


7 21 40 


7 35 40 


7 49 40 


0.3 


4 45 50 


4 55 20 


5 04 50 


5 14 10 


0.4 


3 34 30 


3 41 40 


3 48 50 


3 56 00 


0.5 


2 51 40 


2 57 30 


3 03 10 


3 08 50 


0.6 


2 23 10 


2 27 50 


2 32 40 


2 37 30 


0.7 


2 02 40 


2 06 50 


2 10 50 


2 15 00 


0.8 


1 47 20 


1 51 00 


1 54 30 


1 58 10 


0.9 


1 35 30^ 


1 38 40 


1 41 50 


1 45 00 


1.0 


1 26 00 


1 28 50 


1 31 40 


1 34 30 


1.1 


1 18 10 


1 20 49 


1 23 20 


1 26 00 


1.2 


1 11 40 


1 14 00 


1 16 20 


1 18 50 


1.3 


1 06 10 


1 08 20 


1 10 30 


1 12 40 


1.4 


1 01 20 


1 03 30 


1 05 30 


1 07 30 


1.5 


57 20 


59 10 


1 01 10 


1 03 00 


1.6 


53 40 


55 30 


57 20 


59 00 


1.7 


50 30 


52 10 


53 50 


55 40 


1.8 


47 40 


49 20 


51 00 


52 30 


1.9.. 


45 10 


46 40 


48 10 


49 40 


2.0 


43 00 


44 20 


45 50 


47 20 



THE XAVIGATOR S POCKET-BOOK 



1G5 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 

Miles 
and Tenths. 


Height of Light Above Sea-Level. 


150 Feet. 


155 Feet. 


160 Feet, 


165 Feet. 


2.1 

2.2 

2.3 . 


o t if 

40 50 
39 00 
37 20 
35 50 
34 20 


o / // 

42 20 
40 20 
38 40 
37 00 
35 30 


o / // 

43 40 
41 40 
39 50 
38 10 
36 40 


o / // 

45 00 
43 00 
41 10 
39 20 
37 50 


2.4 

2.5 


2.6 

2.7 

2.8 

2.9 

3.0 


33 00 
31 50 
30 40 
29 40 

28 40 


34 10 
32 50 
31 40 
30 40 
29 40 


35 20 

34 00 
32 40 
31 40 
30 30 


36 20 
35 00 
33 50 
32 40 
31 30 


3.1 

3.2 

3.3....... 

3.4 

3.5 


27 40 
26 50 
26 00 
25 20 
24 30 


28 40 
27 40 
26 50 
26 10 
25 20 


29 30 

28 40 

27 50 
27 00 
26 10 


30 30 

29 30 
28 40 
27 50 

27 00 


3.6 

3.7 

3.9 

4.0 


23 50 
23 10 
22 40 

22 00 
21 30 


24 40 
24 00 
23 20 

22 50 
22 10 


25 30 
24 50 
24 10 
23 30 
22 50 


26 20 
25 30 
24 50 
24 10 
23 40 



166 



THE NAVIGATOR'S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig- 


lit of Light Above Sea-Level. 


Miles 
and Tenths. 




















170 Feet. 


175 Feet. 


180 Feet. 


185 Feet. 




O / It 


o / // 


o r rr 


o r rr 


0.1 


15 49 10 


16 15 40 


16 42 00 


17 08 10 


0.2 


8 03 50 


8 17 50 


8 31 50 


8 45 50 


0.3 


5 23 40 


5 33 10 


5 42 40 


5 52 00 


0.4 


4 03 10 


4 10 10 


4 17 20 


4 24 30 


0.5 


3 14 40 


3 20 20 


3 26 00 


3 31 40 


0.6 


2 42 10 


2 47 00 


2 51 40 


2 56 30 


0.7 


2 19 00 


2 23 10 


2 27 10 


2 31 20 


0.8 


2 01 40 


2 05 20 


2 08 50 


2 12 30 


0.9 


1 48 10 


1 51 20 


1 54 30 


1 57 40 


1.0 


1 37 20 


1 40 10 


1 43 10 


1 46 00 


1.1 


1 28 30 


1 31 10 


1 33 40 


1 36 20 


1.2 


1 21 10 


1 23 30 


1 26 00 


1 28 20 


1.3 


1 14 50 


1 17 10 


1 19 20 


1 21 30 


1.4 


1 09 30 


1 11 40 


1 13 40 


1 15 40 


1.5 


1 05 00 


1 06 50 


1 08 40 


1 10 40 


1.6 


1 00 50 


1 02 40 


1 04 30 


1 06 10 


1.7 


57 20 


59 00 


1 00 40 


1 02 20 


1.8 


54 10 


55 40 


57 20 


58 50 


1.9 


51 20 


52 50 


54 20 


55 50 


2.0 


48 40 


50 10 


51 30 


53 00 



THE XAVIGATOR S POCKET-BOOK 



16? 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heigl 


it of Light Above Sea-Level. 


Allies 










and Tenths. 












170 Feet. 


175 Feet. 


180 Feet. 


185 Feet. 




o i tr 


Of// 


1 It 


or// 


2.1 


46 20 


47 40 


49 10 


50 30 


2.2 


44 20 


45 30 


46 50 


48 10 


2.3 


42 20 


43 40 


44 50 


46 00 


2.4 


40 30 


41 50 


43 00 


44 10 


2.5 


39 00 


40 10 


41 10 


42 20 


2.6 


37 30 


38 30 


39 40 


40 50 


2.7 


36 00 


37 10 


38 10 


39 10 


2.8 


34 50 


35 50 


36 50 


37 50 


2.9 


33 30 


34 30 


35 30 


36 30 


3.0 


32 30 


33 20 


34 20 


35 20 


3.1 


31 20 


32 20 


33 20 


34 10 


3.2 


30 30 


31 20 


32 10 


33 10 


3.3 


29 30 


30 20 


31 10 


32 10 


3.1 


28 40 


29 30 


30 20 


31 10 


3.5 


27 50 


28 40 


29 30 


30 20 


3.6 


27 00 


27 50 


28 40 


29 30 


3.7 


26 20 


27 10 


27 50 


28 40 


3.8 


25 40 


26 20 


27 10 


27 50 


3.9 


25 00 


25 40 


26 30 


27 10 


4.0 


24 20 


25 00 


25 50 


26 30 



108 



THE NAVIGATOR S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Height of Light Above Sea- Level. 


Miles 








and Tenths. 


190 Feet. 


195 Feet. 


200 Feet. 


205 Feet. 




1 If 


o / ft 


o r ft j o / // 


0.1 


17 34 20 


18 00 10 


18 26 10 18 51 50 


0.2 


8 59 50 


9 13 50 


9 27 40 


9 41 40 


3 


6 01 30 
4 31 30 


6 11 00 
4 38 40 


6 20 20 
4 45 50 


6 29 50 
4 53 00 


0.4 


0.5 


3 37 30 


3 43 10 


3 48 50 


3 54 30 


0.6 


3 01 20 


3 06 00 


3 10 50 


3 15 30 


0.7 


2 35 20 


2 39 30 


2 43 30 


2 47 40 


0.8 


2 16 00 


2 19 30 


2 23 10 


2 26 40 


0.9 


2 00 50 


2 04 00 


2 07 20 


2 10 30 


1.0 


1 48 50 


1 51 40 


1 45 30 


1 57 20 


1.1 


1 39 00 


1 41 30 


1 44 10 


1 46 40 


1.2 


1 30 40 


1 33 00 


1 35 30 


1 37 50 


1.3 


1 23 40 


1 26 00 


1 28 10 


1 30 20 


1.4 


1 17 40 


1 19 50 


1 21 50 


1 23 50 


1.5 


1 12 30 


1 14 30 


1 16 20 


1 18 20 


1.6 


1 08 00 


1 09 50 


1 11 40 


1 13 20 


1.7 


1 04 00 


1 05 40 


1 07 20 


1 09 00 


1.8 


1 00 30 


. 1 02 00 


1 03 40 


1 05 10 


1.9 


57 20 


58 50 


1 00 20 


1 01 50 


2.0 


54 30 


55 50 


57 20 


58 40 



THE NAVIGATOR S POCKET-BOOK 



169 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


'lit of Light Above Sea-Level. 


Miles 








and Tenths. 


190 Feet. 


195 Feet. 


200 Feet. 


205 Feet. 




Q t tf 


o r tf 


Q t ft 


O / tf 


2.1 


51 50 


53 10 


54 30 


56 00 


2.2 


49 30 


50 50 


52 00 


53 20 


2.3 


47 20 


48 30 


49 50 


51 00 


2.4 


45 20 


46 30 


47 40 


49 00 


2.5 


43 30 


44 40 


45 50 


47 00 


2.6 


41 50 


43 00 


44 00 


45 10 


2.7 


40 20 


41 20 


42 30 


43 30 


2.8 


38 50 


39 50 


40 50 


42 00 


2.9 


37 30 


38 30 


39 30 


40 30 


3.0 


36 20 


37 10 


38 10 


39 10 


3.1 


35 10 


36 00 


37 00 


37 50 


3.2 


34 00 


34 50 


35 50 


36 40 


3.3 


33 00 


33 50 


34 40 


35 40 


3.4 


32 00 


32 50 


33 40 


34 30 


3.5 


31 10 


31 50 


32 40 


33 30 


3.6 


30 10 


31 00 


31 50 


32 40 


3.7 


29 20 


30 10 


31 00 


31 40 


3.8 


28 40 


29 20 


30 10 


30 50 


3.9 


27 50 


28 40 


29 20 


30 10 


4.0 


27 10 


28 00 


28 40 


29 20 



170 



THE NAVIGATOR S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Height of Light Above Sea-Level. 


Miles 
and Tenths. 


















210 Feet. 


215 Feet. 


220 Feet. 


225 Feet. 




O f ft 


O f If 


O t It 


O t It 


0.1 


19 17 20 


19 42 50 


20 08 10 


20 30 20 


0.2 


9 56 00 


10 09 30 


10 23 20 


10 37 10 


0.3 


6 39 20 


6 48 40 


6 58 10 


7 07 30 


0.4 


5 00 00 


5 07 10 


5 14 10 


5 21 20 


0.5 


4 00 10 


4 06 00 


4 11 40 


4 17 20 


0.6 


3 20 20 


3 25 00 


3 29 50 


3 34 30 


0.7 


2 51 40 


2 55 50 


2 59 50 


3 04 00 


0.8 


2 30 20 


2 33 50 


2 37 30 


2 41 00 


0.9 


2 13 40 


2 16 50 


2 20 00 


2 23 10 


1.0 


2 00 20 


2 03 10 


2 06 00 


2 08 50 


1.1 


1 49 20 


1 52 00 


1 54 30 


1 57 10 


1.2 


1 40 10 


1 42 40 


1 45 00 


1 47 20 


1.3 


1 32 30 


1 34 40 


1 37 00 


1 39 10 


1.4 


1 26 00 


1 28 00 


1 30 00 


1 32 00 


1.5 


1 20 10 


1 22 10 


1 24 00 


1 26 00 


1.6 


1 15 10 


1 17 00 


1 18 50 


1 20 30 


1.7 


1 10 50 


1 12 30 


1 14 10 


1 15 50 


1.8 


1 06 50 


1 08 30 


1 10 00 


1 11 40 


1.9 


1 03 20 


1 04 50 


1 06 20 


1 07 50 


2.0 


1 00 10 


1 01 30 


1 03 00 


1 04 30 



THE NAVIGATOR'S POCKET-BOOK 



171 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance iu 


Heig 


it of Light Above Sea-L 


evel. 


Aliles 










and Tenths. 












210 Feet. 


215 Feet. 


220 Feet. 


225 Feet. 




O t f 


O f ff 


o f ff 


O f ff 


2.1 


57 20 


58 40 


1 00 00 


1 01 20 


2.2 


54 40 


56 00 


57 20 


58 40 


2.3 


52 20 


53 30 


54 50 


66 00 


2.1 


50 10 


51 20 


52 30 


53 40 


2.5 


48 10 


49 20 


50 20 


51 30 


2.6 


46 20 


47 20 


48 30 


49 30 


2.7 


44 30 


45 40 


46 40 


47 40 


2.8 


43 00 


44 00 


45 00 


46 00 


2.9 


41 30 


42 30 


43 30 


44 30 


3.0 


40 10 


41 00 


42 00 


43 00 


3.1 


38 50 


39 40 


40 40 


41 40 


3.2 


37 40 


38 30 


39 20 


40 20 


3.3 


36 30 


37 20 


38 10 


39 00 


3.4 


35 20 


36 10 


37 00 


37 50 


3.5 


34 20 


35 10 


36 00 


36 50 


3.6 


33 20 


34 10 


35 00 


35 50 


3.7 


32 30 


33 20 


34 00 


34 50 


3.8 


31 40 


32 20 


33 10 


33 50 


3.9 


30 50 


31 30 


32 20 


33 00 


4.0 


30 00 


30 50 


31 30 


32 10 



172 



THE NAVIGATOR S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


tit of Light Above Sea-Level. 


Miles 










and Tenths. 


230 Feet. 


235 Feet. 


240 Feet, 


245 Feet. 




o / rt 


O f ft 


o / tr 


O ' // 


0.1 


20 58 20 


21 23 20 


21 48 00 


22 12 40 


0.2 


10 51 00 


11 04 50 


11 18 40 


11 32 20 


0.3 


7 16 50 


7 26 20 


7 35 40 


7 45 00 


0.4 


5 28 30 


5 35 30 


5 42 40 


5 49 40 


0.5. 


4 23 00 


4 28 40 


4 34 30 


4 40 10 


0.6 


3 39 20 


3 44 00 


3 48 50 


3 53 40 


0.7 


3 08 00 


3 12 10 


3 16 10 


3 20 20 


0.8....... 


2 44 40 


2 48 10 


2 51 40 


2 55 20 


0.9 


2 26 20 


2 29 30 


2 32 40 


2 35 50 


1.0 


2 11 40 


2 14 30 


2 17 30 


2 20 20 


1.1 


1 59 40 


2 02 20 


2 05 00 


2 07 30 


1.2 


1 49 50 


1 52 10 


1 54 30 


1 57 00 


1.3 


1 41 20 


1 43 30 


1 45 40 


1 48 00 


1.4 


1 34 10 


1 36 10 


1 38 10 


1 40 10 


1.5 


1 27 50 


1 29 40 


1 31 40 


1 33 30 


1.6 


1 22 20 


1 24 10 


1 26 00 


1 27 40 


1.7 


1 17 30 


1 19 10 


1 20 50 


1 22 30 


1.8 


1 13 10 


1 14 50 


1 16 20 


1 18 00 


1.9 


1 09 20 
1 05 50 


1 10 50 

1 07 20 


1 12 20 
1 08 40 


1 13 50 
1 10 10 


2.0 



THE NAVIGATOR S POCKET-BOOK 



173 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


lit of Light Above Sea-Level. 


Miles 










and Tenths. 












230 Feet. 


235 Feet, 


240 Feet. 


245 Feet. 




0/1/ 


o / // 


O / // 


O / // 


2.1 


1 02 40 


1 04 10 


1 05 30 


1 06 50 


2.2 


59 50 


1 01 10 


1 02 30 


1 03 50 


2.3 


57 20 


58 30 


59 50 


1 01 00 


2.4 


54 50 


56 10 


57 20 


58 30 


2.5 


52 40 


53 50 


55 00 


56 10 


2.6 


50 40 


51 50 


52 50 


54 00 


2.7 


48 50 


49 50 


51 00 


52 00 


2.8 


47 00 


48 00 


49 10 


50 10 


2.9 


45 30 


46 30 


47 20 


48 20 


3.0 


43 50 


44 50 


45 50 


46 50 


3.1 


0. 42 30 


43 30 


44 20 


45 20 


3.2 


41 10 


42 00 


43 00 


44 00 


3.3 


40 00 


40 50 


41 40 


42 30 


3.4 


38 40 


39 40 


40 30 


41 20 


3.5 


37 40 


38 30 


39 20 


40 10 


3.G 


36 40 


37 20 


38 10 


39 00 


3.7... 


35 40 


36 20 


37 10 


38 00 


3.8 


34 40 


35 30 


36 10 


37 00 


3.9 


33 50 


34 30 


35 10 


36 00 


4.0 


33 00 


33 40 


34 20 


35 10 



174 



THE NAVIGATOR'S POCKET-BOOK 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 


Heig 


it of Light Above Sea-Level. 


Miles 










and Tenths. 












250 Feet. 


260 Feet. 


270 Feet. 


280 Feet, 




O t It 


O / // 


O ' // 


/ // 


0.1 


22 37 10 


23 25 40 


24 13 40 


25 01 00 


0.2 


11 46 10 


12 13 30 


12 40 50 


13 08 00 


0.3 


7 54 30 


8 13 10 


8 31 50 


8 50 30 


0.4 


5 56 50 


6 11 00 


6 25 10 


6 39 20 


0.5 


4 45 50 


4 57 10 


5 08 30 


5 20 00 


0.6 


3 58 20 


4 07 50 


4 17 20 


4 26 50 


0.7 


3 24 20 


3 32 30 


3 40 40 


3 48 50 


0.8 


2 58 50 


3 06 00 


3 13 10 


3 20 20 


0.9 


2 39 00- 


2 45 20 


2 51 40 


2 58 10 


1.0 


2 23 10 


2 28 50 


2 34 40 


2 40 20 


1.1 


2 10 10 


2 15 20 


2 20 30 


2 25 40 


1.2 


1 59 20 


2 04 10 


2 08 50 


2 13 40 


1.3 


1 50 10 


1 54 30 


1 59 00 


2 03 20 


1.4 


1 42 20 


1 46 20 


1 50 30 


1 54 30 


1.5 


1 35 30 


1 39 20 


1 43 10 


1 46 50 


1.6 


1 29 30 


1 33 00 


1 36 40 


1 40 10 


1.7 


1 24 10 


1 27 40 


1 31 00 


1 34 20 


1.8 


1 19 30 


1 22 40 


1 26 00 


1 29 10 


1.9 


1 15 20 


1 18 20 


1 21 20 


1 24 30 


2.0 


1 11 40 


1 14 30 


1 17 20 


1 20 10 



THE NAVIGATOR S POCKET-BOOK 



175 



PATTERSON'S DANGER- ANGLE TABLES. 


Distance in 


Height of Light Above Sea-Level. 


Miles 










and Tenths. 












250 Feet. 


260 Feet. 


270 Feet, 


280 Feet. 




O 1 It 


ota 


o / // 


o / // 


2.1 


1 08 10 


1 11 00 


1 13 40 


1 16 20 


2.2 


1 05 10 


1 07 40 


1 10 20 


1 12 50 


2.3 


1 02 20 


1 04 50 


1 07 10 


1 09 40 


2.4 


59 40 


1 02 00 


1 04 30 


1 06 50 


2.5 


57 20 


59 30 


1 01 50 


1 04 10 


2.6 


55 00 


57 20 


59 30 


1 01 40 


2.7 


53 00 


55 10 


57 20 


59 20 


2.8 


51 10 


53 10 


55 10 


57 20 


2.9 


49 20 


51 20 


53 20 


55 20 


3.0 


47 40 


49 40 


51 30 


53 30 


3.1 


46 10 


48 00 


49 50 


51 40 


3.2 


44 50 


46 30 


48 20 


50 10 


3.3 


43 20 


45 10 


46 50 


48 40 


3.4 


42 10 


43 50 


45 30 


47 10 


3.5 


40 50 


42 30 


44 10 


45 50 


3.6 


39 50 


41 20 


43 00 


44 30 


3.7 


38 40 


40 20 


41 50 


43 20 


3.8 


37 40 


39 10 


40 40 


42 10 


3.9 


36 40 


38 10 


39 40 


41 10 


4.0 


35 50 


37 10 


38 40 


40 10 



176 



THE KAVIGATOR S POCKET-BOOK 



PATTERSON'S DANGEPv-ANGLE TABLES. 


Distance in 


Heig 1 


it of Light Above Sea-Level. 


Miles 










and Tenths. 












290 Feet. 


300 Feet. 


310 Feet, 


320 Feet. 




Of// 


o r ir 


o / II 


Of n 


0.1....... 


25 30 00 


26 15 50 


27 01 00 


27 45 30 


0.2 


13 24 50 


13 51 30 


14 18 10 


14 44 40 


0.3 


9 02 00 


9 20 20 


9 38 40 


9 57 00 


0.4 


6 48 00 


7 02 00 


7 15 50 


7 29 40 


0.5 


5 27 00 


5 38 10 


5 49 20 


6 00 30 


0.6 


4 32 40 


4 42 00 


4 51 30 


5 00 50 


0.7.. 


3 53 50 


4 01 50 


4 10 00 


4 18 00 


0.8 


3 24 40 


3 31 50 


3 38 50 


3 45 50 


0.9 


3 02 00 


3 08 20 


3 14 30 


3 20 50 


1.0 


2 43 50 


2 49 30 


2 55 10 


3 00 50 


1.1 


2 29 00 


2 34 10 


2 39 10 


2 44 20 


1.2 


2 16 30 


2 21 20 


2 26 00 


2 30 40 


1.3 


2 06 00 


2 10 20 


2 14 50 


2 19 10 


1.4 


1 57 00 


2 01 10 


2 05 10 


2 09 10 


1.5 


1 49 20 


1 53 00 


1 56 50 


2 00 30 


1.6 


1 42 30 


1 46 00 


1 49 30 


1 53 00 


1.7 


1 36 30 


1 39 40 


1 43 00 


1 46 20 


1.8 


1 31 00 


1 34 10 


1 37 20 


1 40 30 


1.9 


1 26 20 


1 29 10 


1 32 10 


1 35 10 


2.0 


1 22 00 


1 24 50 


1 27 40 


1 30 30 



THE NAVIGATOR S POCKET-BOOK 



177 



PATTERSON'S DANGER-ANGLE TABLES. 


Distance in 

Miles 
and Tenths. 


Height of Light Above Sea-Level. 


290 Feet. 


300 Feet. 310 Feet. 


320 Feet, 


2.1 

2.2 

2.3 

2.4 

2.5 


/ ft 

1 18 00 
1 14 30 
1 11 20 
1 08 20 
1 05 30 


Q f ff 

1 20 50 
1 17 00 
1 13 40 
1 10 40 

1 07 50 


/ ff 

1 23 30 
1 19 40 
1 16 10 
1 13 00 
1 10 10 


f ff 

1 26 10 
1 22 10 
1 18 40 
1 15 20 
1 12 20 


2.6 

2.7 

2.8 

2.9 


1 03 00 
1 00 40 
58 30 
56 30 
54 40 


1 05 10 
1 02 50 
1 00 30 
58 30 
56 30 


1 07 20 
1 04 50 
1 02 40 
1 00 30 

58 20 


1 09 30 
1 07 00 
1 04 40 
1 02 20 

1 00 20 


3.0 


3.1 

3.2 

3.3 

3.4 

3.5 


52 50 
51 10 
49 40 

48 10 
46 50 


54 40 
53 00 
51 20 

49 50 
48 30 


b6 30 
54 50 
53 10 
51 30 

50 00 


58 20 
56 30 
54 50 
53 10 
51 40 


3.6 ..". 

3.7 

3.8 

3.9 

4.0 


45 30 
44 20 
43 10 
42 00 
41 00 


47 10 
45 50 
44 40 
43 30 
42 20 


48 40 
47 20 
46 10 
45 00 
43 50 


50 10 
48 50 
47 40 
46 20 
45 10 



12 



^ / <? 8 



■-^TnpiyrrG^gC 



